Fix mismanagement in handling of temporary scanline for vertical flip.

BUG=116637
TEST=manual test from bug report with ASAN

Review URL: https://chromiumcodereview.appspot.com/9617038

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@125301 0039d316-1c4b-4281-b951-d872f2087c98
WebGLId WebGraphicsContext3DCommandBufferImpl::getPlatformTextureId() {
  return context_->GetParentTextureId();
}

WebGLId WebGraphicsContext3DCommandBufferImpl::getPlatformTextureId() {
  return context_->GetParentTextureId();
}
