Change the PepperInProcessRouter to defer resource destruction messages.
This changes the in process "proxy" so it posts tasks to send resource destruction messages
instead of calling them directly. This prevents several kinds of reentrancy into the plugin-side
code. In this case, when a URLLoader is released, the plugin can finish before the host cancels
the load and potentially deletes the instance.
BUG=276368
Review URL: https://chromiumcodereview.appspot.com/
23688004
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@222614 0039d316-1c4b-4281-b951-d872f2087c98