function stubSpdyCheck(spdyEnabled) {
  stubs.set(
      ForwardChannelRequestPool, 'isSpdyOrHttp2Enabled_', () => spdyEnabled);
}
Stubs
ForwardChannelRequestPool.isSpdyOrHttp2Enabled_ to
manage the max pool size for the forward channel.
@param {boolean} spdyEnabled Whether SPDY is enabled for the test.