deferFirstFrameReport method
Tell the framework not to report the frame it is building as a "useful" first frame until there is a corresponding call to allowFirstFrameReport.
This is used by WidgetsApp to report the first frame.
Implementation
//
// TODO(ianh): This method should only be available in debug and profile modes.
void deferFirstFrameReport() {
assert(_deferFirstFrameReportCount >= 0);
_deferFirstFrameReportCount += 1;
}