Use a dark titlebar when we've requested dark theme (#14536)

This applies to `"showTabsInTitlebar": false,`. We literally never set that for the `IslandWindow` before, only ever the NCIW. 

Closes #11589


![update-titlebar-for-theme](https://user-images.githubusercontent.com/18356694/207109370-a63a8b19-4c42-4b1f-8d39-8c3abdf1b403.gif)


For a dramatic example - here's the IW with mica enabled, in dark mode:

![image](https://user-images.githubusercontent.com/18356694/207109465-a6165637-31a5-45a4-bff0-51ac79404cd6.png)

Theme json:

```json
        {
            "name": "chonk",
            "tab":
            {
                "background": "#00000000",
                "unfocusedBackground": "#00000000",
                "showCloseButton": "never"
            },
            "tabRow":
            {
                "background": "#00000000",
                "unfocusedBackground": "#00000000",
            },
            "window":
            {
                "applicationTheme": "dark",
                "useMica": true
            }
        },
```

src/cascadia/TerminalSettingsModel/GlobalAppSettings.cpp

@@ -6,7 +6,6 @@
 #include "../../types/inc/Utils.hpp"
 #include "JsonUtils.h"
 #include "KeyChordSerialization.h"
-#include "SettingsUtils.h"
 
 #include "GlobalAppSettings.g.cpp"
 
@@ -213,7 +212,7 @@ Json::Value GlobalAppSettings::ToJson() const
 
 winrt::Microsoft::Terminal::Settings::Model::Theme GlobalAppSettings::CurrentTheme() noexcept
 {
-    auto requestedTheme = IsSystemInDarkTheme() ?
+    auto requestedTheme = Model::Theme::IsSystemInDarkTheme() ?
                               winrt::Windows::UI::Xaml::ElementTheme::Dark :
                               winrt::Windows::UI::Xaml::ElementTheme::Light;
 

src/cascadia/TerminalSettingsModel/Microsoft.Terminal.Settings.ModelLib.vcxproj

@@ -115,7 +115,6 @@
     <ClInclude Include="WslDistroGenerator.h" />
     <ClInclude Include="SshHostGenerator.h" />
     <ClInclude Include="ModelSerializationHelpers.h" />
-    <ClInclude Include="SettingsUtils.h" />
   </ItemGroup>
   <!-- ========================= Cpp Files ======================== -->
   <ItemGroup>

src/cascadia/TerminalSettingsModel/TerminalSettings.cpp

@@ -7,21 +7,10 @@
 
 #include "TerminalSettings.g.cpp"
 #include "TerminalSettingsCreateResult.g.cpp"
-#include "SettingsUtils.h"
 
 using namespace winrt::Microsoft::Terminal::Control;
 using namespace Microsoft::Console::Utils;
 
-// I'm not even joking, this is the recommended way to do this:
-// https://learn.microsoft.com/en-us/windows/apps/desktop/modernize/apply-windows-themes#know-when-dark-mode-is-enabled
-bool IsSystemInDarkTheme()
-{
-    static auto isColorLight = [](const winrt::Windows::UI::Color& clr) -> bool {
-        return (((5 * clr.G) + (2 * clr.R) + clr.B) > (8 * 128));
-    };
-    return isColorLight(winrt::Windows::UI::ViewManagement::UISettings().GetColorValue(winrt::Windows::UI::ViewManagement::UIColorType::Foreground));
-};
-
 namespace winrt::Microsoft::Terminal::Settings::Model::implementation
 {
     static std::tuple<Windows::UI::Xaml::HorizontalAlignment, Windows::UI::Xaml::VerticalAlignment> ConvertConvergedAlignment(ConvergedAlignment alignment)
@@ -204,7 +193,7 @@ namespace winrt::Microsoft::Terminal::Settings::Model::implementation
         auto requestedTheme = currentTheme.RequestedTheme();
         if (requestedTheme == winrt::Windows::UI::Xaml::ElementTheme::Default)
         {
-            requestedTheme = IsSystemInDarkTheme() ?
+            requestedTheme = Model::Theme::IsSystemInDarkTheme() ?
                                  winrt::Windows::UI::Xaml::ElementTheme::Dark :
                                  winrt::Windows::UI::Xaml::ElementTheme::Light;
         }

src/cascadia/TerminalSettingsModel/Theme.cpp

@@ -362,3 +362,13 @@ winrt::com_ptr<ThemePair> ThemePair::Copy() const
     pair->_LightName = _LightName;
     return pair;
 }
+
+// I'm not even joking, this is the recommended way to do this:
+// https://learn.microsoft.com/en-us/windows/apps/desktop/modernize/apply-windows-themes#know-when-dark-mode-is-enabled
+bool Theme::IsSystemInDarkTheme()
+{
+    static auto isColorLight = [](const winrt::Windows::UI::Color& clr) -> bool {
+        return (((5 * clr.G) + (2 * clr.R) + clr.B) > (8 * 128));
+    };
+    return isColorLight(winrt::Windows::UI::ViewManagement::UISettings().GetColorValue(winrt::Windows::UI::ViewManagement::UIColorType::Foreground));
+};

src/cascadia/TerminalSettingsModel/Theme.h

@@ -100,6 +100,8 @@ namespace winrt::Microsoft::Terminal::Settings::Model::implementation
 
         winrt::Windows::UI::Xaml::ElementTheme RequestedTheme() const noexcept;
 
+        static bool IsSystemInDarkTheme();
+
         WINRT_PROPERTY(winrt::hstring, Name);
 
         MTSM_THEME_SETTINGS(THEME_SETTINGS_INITIALIZE)

src/cascadia/TerminalSettingsModel/Theme.idl

@@ -78,6 +78,7 @@ namespace Microsoft.Terminal.Settings.Model
 
         // A helper for retrieving the RequestedTheme out of the window property
         Windows.UI.Xaml.ElementTheme RequestedTheme { get; };
+        static Boolean IsSystemInDarkTheme();
 
     }
 }

src/cascadia/WindowsTerminal/AppHost.cpp

@@ -1344,6 +1344,20 @@ winrt::fire_and_forget AppHost::_RenameWindowRequested(const winrt::Windows::Fou
     }
 }
 
+bool _isActuallyDarkTheme(const auto requestedTheme)
+{
+    switch (requestedTheme)
+    {
+    case winrt::Windows::UI::Xaml::ElementTheme::Light:
+        return false;
+    case winrt::Windows::UI::Xaml::ElementTheme::Dark:
+        return true;
+    case winrt::Windows::UI::Xaml::ElementTheme::Default:
+    default:
+        return Theme::IsSystemInDarkTheme();
+    }
+}
+
 void AppHost::_updateTheme()
 {
     auto theme = _logic.Theme();
@@ -1353,6 +1367,12 @@ void AppHost::_updateTheme()
     const auto b = _logic.TitlebarBrush();
     const auto opacity = b ? ThemeColor::ColorFromBrush(b).A / 255.0 : 0.0;
     _window->UseMica(theme.Window() ? theme.Window().UseMica() : false, opacity);
+
+    // This is a hack to make the window borders dark instead of light.
+    // It must be done before WM_NCPAINT so that the borders are rendered with
+    // the correct theme.
+    // For more information, see GH#6620.
+    LOG_IF_FAILED(TerminalTrySetDarkTheme(_window->GetHandle(), _isActuallyDarkTheme(theme.RequestedTheme())));
 }
 
 void AppHost::_HandleSettingsChanged(const winrt::Windows::Foundation::IInspectable& /*sender*/,

src/cascadia/WindowsTerminal/BaseWindow.h

@@ -28,7 +28,7 @@ class BaseWindow
             WINRT_ASSERT(!that->_window);
             that->_window = wil::unique_hwnd(window);
 
-            return that->_OnNcCreate(wparam, lparam);
+            return that->OnNcCreate(wparam, lparam);
         }
         else if (T* that = GetThisFromHandle(window))
         {
@@ -214,7 +214,7 @@ class BaseWindow
     // - This method is called when the window receives the WM_NCCREATE message.
     // Return Value:
     // - The value returned from the window proc.
-    virtual [[nodiscard]] LRESULT _OnNcCreate(WPARAM wParam, LPARAM lParam) noexcept
+    virtual [[nodiscard]] LRESULT OnNcCreate(WPARAM wParam, LPARAM lParam) noexcept
     {
         SetWindowLongPtr(_window.get(), GWLP_USERDATA, reinterpret_cast<LONG_PTR>(this));
 

src/cascadia/WindowsTerminal/IslandWindow.cpp

@@ -1913,3 +1913,29 @@ void IslandWindow::UseMica(const bool newValue, const double /*titlebarOpacity*/
     const int attribute = newValue ? DWMSBT_MAINWINDOW : DWMSBT_NONE;
     std::ignore = DwmSetWindowAttribute(GetHandle(), DWMWA_SYSTEMBACKDROP_TYPE, &attribute, sizeof(attribute));
 }
+
+// Method Description:
+// - This method is called when the window receives the WM_NCCREATE message.
+// Return Value:
+// - The value returned from the window proc.
+[[nodiscard]] LRESULT IslandWindow::OnNcCreate(WPARAM wParam, LPARAM lParam) noexcept
+{
+    const auto ret = BaseWindow::OnNcCreate(wParam, lParam);
+    if (!ret)
+    {
+        return FALSE;
+    }
+
+    // This is a hack to make the window borders dark instead of light.
+    // It must be done before WM_NCPAINT so that the borders are rendered with
+    // the correct theme.
+    // For more information, see GH#6620.
+    //
+    // Theoretically, we don't need this anymore, since _updateTheme will update
+    // the darkness of our window. However, we're keeping this call to prevent
+    // the window from appearing as a white rectangle for a frame before we load
+    // the rest of the settings.
+    LOG_IF_FAILED(TerminalTrySetDarkTheme(_window.get(), true));
+
+    return TRUE;
+}

src/cascadia/WindowsTerminal/IslandWindow.h

@@ -26,6 +26,9 @@ class IslandWindow :
     HWND GetInteropHandle() const;
 
     [[nodiscard]] virtual LRESULT MessageHandler(UINT const message, WPARAM const wparam, LPARAM const lparam) noexcept override;
+
+    [[nodiscard]] LRESULT OnNcCreate(WPARAM wParam, LPARAM lParam) noexcept override;
+
     void OnResize(const UINT width, const UINT height) override;
     void OnMinimize() override;
     void OnRestore() override;

src/cascadia/WindowsTerminal/NonClientIslandWindow.cpp

@@ -1044,27 +1044,6 @@ void NonClientIslandWindow::_UpdateFrameMargins() const noexcept
     return 0;
 }
 
-// Method Description:
-// - This method is called when the window receives the WM_NCCREATE message.
-// Return Value:
-// - The value returned from the window proc.
-[[nodiscard]] LRESULT NonClientIslandWindow::_OnNcCreate(WPARAM wParam, LPARAM lParam) noexcept
-{
-    const auto ret = IslandWindow::_OnNcCreate(wParam, lParam);
-    if (!ret)
-    {
-        return FALSE;
-    }
-
-    // This is a hack to make the window borders dark instead of light.
-    // It must be done before WM_NCPAINT so that the borders are rendered with
-    // the correct theme.
-    // For more information, see GH#6620.
-    LOG_IF_FAILED(TerminalTrySetDarkTheme(_window.get(), true));
-
-    return TRUE;
-}
-
 // Method Description:
 // - Called when the app wants to change its theme. We'll update the frame
 //   theme to match the new theme.

src/cascadia/WindowsTerminal/NonClientIslandWindow.h

@@ -81,7 +81,6 @@ class NonClientIslandWindow : public IslandWindow
     int _GetTopBorderHeight() const noexcept;
     LRESULT _dragBarNcHitTest(const til::point pointer);
 
-    [[nodiscard]] LRESULT _OnNcCreate(WPARAM wParam, LPARAM lParam) noexcept override;
     [[nodiscard]] LRESULT _OnNcCalcSize(const WPARAM wParam, const LPARAM lParam) noexcept;
     [[nodiscard]] LRESULT _OnNcHitTest(POINT ptMouse) const noexcept;
     [[nodiscard]] LRESULT _OnPaint() noexcept;