Switch Extensions::TabHelper to use WebContents, WebContentsUserData.

BUG=107201
TEST=no visible change
[email protected]

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=155743

Reverted: http://src.chromium.org/viewvc/chrome?view=rev&revision=155901

Review URL: https://chromiumcodereview.appspot.com/10917026

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@156366 0039d316-1c4b-4281-b951-d872f2087c98
44 files changed