Added performance instrumentation for compositing addToScene() calls (#3885)
Added performance instrumentation for compositing addToScene() calls (#3885)

* Added performance instrumentation for compositing addToScene() calls.

* Switched to non-callback versions of the Timeline API.

* Fixed Dart formatting nit.

flutter/flutter,cbracken/flutter,Hixie/flutter,cbracken/flutter,tvolkert/flutter,tvolkert/flutter,turnidge/flutter,tvolkert/flutter,Hixie/flutter,flutter/flutter,tvolkert/flutter,Hixie/flutter,tvolkert/flutter,turnidge/flutter,flutter/flutter,aghassemi/flutter,aghassemi/flutter,flutter/flutter,aghassemi/flutter,Hixie/flutter,cbracken/flutter,Hixie/flutter,Hixie/flutter,tvolkert/flutter,cbracken/flutter,Hixie/flutter,cbracken/flutter,flutter/flutter,tvolkert/flutter,turnidge/flutter,cbracken/flutter,tvolkert/flutter,aghassemi/flutter,turnidge/flutter,Hixie/flutter,flutter/flutter,tvolkert/flutter,cbracken/flutter,flutter/flutter,cbracken/flutter,turnidge/flutter,tvolkert/flutter,flutter/flutter,cbracken/flutter,flutter/flutter,Hixie/flutter,cbracken/flutter,flutter/flutter,Hixie/flutter