Moved extension_api to src/extensions/common

This is part of the move of extensions code into the extensions
component. This change does not move the generated API data and API
resources.

[email protected]
BUG=162530

Review URL: https://codereview.chromium.org/50743005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@232345 0039d316-1c4b-4281-b951-d872f2087c98
17 files changed