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::didDownloadData(WebURLLoader* loader,
                                         int data_length) {
  bytes_received_ += data_length;
  UpdateStatus();
}

void PPB_URLLoader_Impl::didDownloadData(WebURLLoader* loader,
                                         int data_length) {
  bytes_received_ += data_length;
  UpdateStatus();
}
