Add support for distilling current WebContents

This CL adds the utilities needed for using the current WebContents when
distilling web pages.

BUG=361939

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=272611

Review URL: https://codereview.chromium.org/266073003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@273101 0039d316-1c4b-4281-b951-d872f2087c98
24 files changed