- added the channel implementation,
- added inspector implementation,
- added v8::Extension for communication between backend and frontend.

BUG=chromium:635948
R=dgozman@chromium.org,alph@chromium.org

Committed: https://crrev.com/cceaa1225c6a96a28d2c7410d1db520423fb8c31
Review-Url: https://codereview.chromium.org/2368393003
Cr-Original-Commit-Position: refs/heads/master@{#39888}
Cr-Commit-Position: refs/heads/master@{#39928}