Ensure com_google_api's service protos are correctly built

[davemasselink]

Add a test case for exercising ES6 generation of proto files using the extend keyword.

Builds on work in protobuf-javascript repo: PR#8

[egormodin]

isn't it correctly build now, so nothing is failed? would it be better to simulate a case where we are failed. I mean create proto which using extend feature and create a ts test case where it is being used.

[davemasselink]

yes, I think you're right

initially I thought the issue might come up in puling in much of the same dependency chain but as you say, that doesn't highlight the issue

creating a new proto using extend keyword to test now

[davemasselink]

ready for your to merge, if and when you feel comfortable doing so, @gonzojive. thanks