PPAPI: Make CompletionCallbacks work right on background threads.

Now, TrackedCallback::Run will:
-Run the callback immediately if it is on the right thread.
-PostRun to the correct thread if it is not.

This was preceded by https://chromiumcodereview.appspot.com/10909244/, which removed ClearAndRun and does some other little cleanups to TrackedCallback to make it usable on background threads.


BUG=92909

Review URL: https://chromiumcodereview.appspot.com/10910099

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@166719 0039d316-1c4b-4281-b951-d872f2087c98
26 files changed