Convert plugin and GPU process to brokered handle duplication.

BUG=119250
Review URL: https://chromiumcodereview.appspot.com/9958034

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@132303 0039d316-1c4b-4281-b951-d872f2087c98
 int WebGraphicsContext3DCommandBufferImpl::GetChannelID() {
  return host_ ? host_->client_id() : 0;
}

 int WebGraphicsContext3DCommandBufferImpl::GetChannelID() {
  return host_ ? host_->client_id() : 0;
}
