* Mention Goma for Googlers in CONTRIBUTING.md

* review comments

* Removed 'pub get' from the instructions

According to Hixie, 'pub get' is abstracted into flutter packages upgrade, and so there shouldn't be a need to run pub get directly.

* Removed pub get lines entirely.

* Document the need to sync the engine repo to avoid #8005

* Flit gclient sync and git pull

Fixes https://github.com/flutter/flutter/issues/7294

* Mention updating the buildroot git remotes

I always forget how to do this...

* Update CONTRIBUTING.md

unzip is missing from documentation and is required to run 
"gclient sync"  successfully. Unzip does not come installed by default
on every Linux installations.
Signed-off-by: NPhilippe Ombredanne <pombredanne@nexb.com>

At some point recently we started putting a JSON file in the out/ directory and this broke this suggested build script.
This patch makes the script more resilient to such files.

Originally, this was a step that had to be carried out manually. Presumably because we did not want developers to download the Android SDK and NDK if they were not targetting Android. In practice, this is rarely the case. Even the buildbots unconditionally run the script (though they don’t need Android artifacts on the Mac since there is no Mac to Android builder).

Have the sample build script exit after the first failed build.

Added a section which explains how to get `dart:ui` changes.

We still need this for the observatory build.

This reverts commit 5082974b.

The engine.git repo doesn't need a copy of the Dart SDK anymore.

Fixes https://github.com/flutter/flutter/issues/2618

* Updating CONTRIBUTING.md to mention latest paths

* Update CONTRIBUTING.md

Fixes #https://github.com/flutter/flutter/issues/3689

These commands are the same, but `run` is the new hotness.

Mention the waterfall and conventions around it.

Depends on https://github.com/flutter/website/pull/177

Sample code is not differentiated enough to disambiguate the full stop at the end of the line.