Maintain a map of all resources in the resource tracker and clear instance back pointers when needed,

BUG=85808
Review URL: http://codereview.chromium.org/7196001

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@89746 0039d316-1c4b-4281-b951-d872f2087c98
void PPB_URLLoader_Impl::RunCallback(int32_t result) {
  if (!pending_callback_.get()) {
    return;
  }

  scoped_refptr<TrackedCompletionCallback> callback;
  callback.swap(pending_callback_);
  callback->Run(result);  // Will complete abortively if necessary.
}

void PPB_URLLoader_Impl::RunCallback(int32_t result) {
  if (!pending_callback_.get()) {
    return;
  }

  scoped_refptr<TrackedCompletionCallback> callback;
  callback.swap(pending_callback_);
  callback->Run(result);  // Will complete abortively if necessary.
}
