Implement DevTools ScreenCast support for Android WebView

As WebView uses synchronous compositor, regular Chrome code doesn't work.
This patch adds necessary plumbing. Screen capturing is implemented via the software path.

BUG=323127

Review URL: https://codereview.chromium.org/88613002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@238676 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 238676