GitLab

- Introduce ExtensionHost, which is the guy that talks to the RenderViewHost.
- ExtensionView holds an ExtensionHost, and also renders its contents in an
  HWND.
- Added code to load a page optionally specified in the manifest as a
  background process whenever it exists.
Review URL: http://codereview.chromium.org/92043

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@14902 0039d316-1c4b-4281-b951-d872f2087c98