Call show paste options in context menu (if clipboard has contents)

This was a regression that I unintentionally introduced with 40fc107

Fixes #8000

Auditors: @lukemulks, @alexwykoff

Test Plan:
1. Visit a page with a text box (ex: create an issue on browser-laptop)
2. Type text into a textbox
3. Use the mouse to select and cut the text
4. Right click to open a context menu inside the textbox
5. You should now see paste again

Author: bsclifton

js/contextMenus.js

@@ -650,7 +650,7 @@ function getMisspelledSuggestions (selection, isMisspelled, suggestions) {
 }
 
 function getEditableItems (selection, editFlags, hasFormat) {
-  const hasSelection = selection.length > 0
+  const hasSelection = selection && selection.length > 0
   const hasClipboard = clipboard.readText().length > 0
   const template = []
 
@@ -1026,10 +1026,7 @@ function mainTemplateInit (nodeProps, frame, tab) {
       }
     }
 
-    const editableItems = nodeProps.selectionText
-      ? getEditableItems(nodeProps.selectionText, nodeProps.editFlags, true)
-      : []
-
+    const editableItems = getEditableItems(nodeProps.selectionText, nodeProps.editFlags, true)
     template.push(...misspelledSuggestions, {
       label: locale.translation('undo'),
       accelerator: 'CmdOrCtrl+Z',

test/unit/js/contextMenusTest.js

@@ -6,6 +6,7 @@
 const mockery = require('mockery')
 const assert = require('assert')
 const sinon = require('sinon')
+const fakeElectron = require('../lib/fakeElectron')
 let fakeElectronMenu
 let contextMenus
 require('../braveUnit')
@@ -21,7 +22,7 @@ describe('Context menu module unit tests', function () {
       warnOnUnregistered: false,
       useCleanCache: true
     })
-    mockery.registerMock('electron', require('../lib/fakeElectron'))
+    mockery.registerMock('electron', fakeElectron)
     mockery.registerMock('../js/l10n', fakeLocale)
     contextMenus = require('../../../js/contextMenus')
     fakeElectronMenu = require('../lib/fakeElectronMenu')
@@ -33,16 +34,35 @@ describe('Context menu module unit tests', function () {
 
   describe('onMainContextMenu', function () {
     describe('when calling mainTemplateInit', function () {
+      let clipboardReadTextSpy
+      let menuBuildFromTemplateSpy
       let menuPopupSpy
       let menuDestroySpy
 
       before(function () {
+        clipboardReadTextSpy = sinon.spy(fakeElectron.remote.clipboard, 'readText')
+        menuBuildFromTemplateSpy = sinon.spy(fakeElectron.remote.Menu, 'buildFromTemplate')
         menuPopupSpy = sinon.spy(fakeElectronMenu, 'popup')
         menuDestroySpy = sinon.spy(fakeElectronMenu, 'destroy')
       })
 
       after(function () {
+        clipboardReadTextSpy.restore()
+        menuBuildFromTemplateSpy.restore()
         menuPopupSpy.restore()
+        menuDestroySpy.restore()
+      })
+
+      it('calls clipboard.readText', function () {
+        clipboardReadTextSpy.reset()
+        contextMenus.onMainContextMenu()
+        assert.equal(clipboardReadTextSpy.calledOnce, true)
+      })
+
+      it('calls Menu.buildFromTemplate', function () {
+        menuBuildFromTemplateSpy.reset()
+        contextMenus.onMainContextMenu()
+        assert.equal(menuBuildFromTemplateSpy.calledOnce, true)
       })
 
       it('calls menu.popup', function () {

test/unit/lib/fakeElectron.js

@@ -15,6 +15,9 @@ const fakeElectron = {
       on: function () {
       }
     },
+    clipboard: {
+      readText: function () { return '' }
+    },
     getCurrentWindow: function () {
       return {
         on: () => {},