Add ChildMessageFilter, a base class for renderer/worker cross-thread MessageFilter

- Save some dup'ed code in similar message filters
- Centralize WorkerRunner thread-handling code into one class (which could be helpful when we migrate worker thread implementation)

BUG=none

Review URL: https://codereview.chromium.org/63843002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@236004 0039d316-1c4b-4281-b951-d872f2087c98
Fixing Chromeos build.

TBR=jochen

BUG=318120

Review URL: https://codereview.chromium.org/64953006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@236005 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 236005
Revert 236005 "Fixing Chromeos build."

> Fixing Chromeos build.
> 
> TBR=jochen
> 
> BUG=318120
> 
> Review URL: https://codereview.chromium.org/64953006

TBR=finnur@chromium.org

Review URL: https://codereview.chromium.org/73733006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@236006 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 236006