Adds RefCountedDeleteOnMessageLoop
RefCountedDeleteOnMessageLoop is similar to RefCountedThreadSafe, but guarantees that
the referenced object will be deleted on the specified loop.
The functionality is similar to content::DeleteOnThread<> but does not depend on
BrowserThread.
The CL includes an example use of the class.
BUG=248049
TBR=stuartmorgan, joth
Review URL: https://chromiumcodereview.appspot.com/
16938006
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@206445 0039d316-1c4b-4281-b951-d872f2087c98