Fix Stack Buffer Overflow in QuicClientPromisedInfo::OnPromiseHeaders

BUG=777728

Cq-Include-Trybots: master.tryserver.chromium.android:android_cronet_tester;master.tryserver.chromium.mac:ios-simulator-cronet
Change-Id: I6a80db88aafdf20c7abd3847404b818565681310
Reviewed-on: https://chromium-review.googlesource.com/748425
Reviewed-by: Zhongyi Shi <zhongyi@chromium.org>
Commit-Queue: Ryan Hamilton <rch@chromium.org>
Cr-Commit-Position: refs/heads/master@{#513105}
void QuicClientPromisedInfo::OnResponseHeaders(const SpdyHeaderBlock& headers) {
  response_headers_.reset(new SpdyHeaderBlock(headers.Clone()));
  if (client_request_delegate_) {
    FinalValidation();
  }
}

void QuicClientPromisedInfo::OnResponseHeaders(const SpdyHeaderBlock& headers) {
  response_headers_.reset(new SpdyHeaderBlock(headers.Clone()));
  if (client_request_delegate_) {
    FinalValidation();
  }
}
