Add option to track when we're showing blankness during fast scrolling

Summary:
If tracking is enabled and the sampling check passes on a scroll or layout event,
we compare the scroll offset to the layout of the rendered items. If the items don't cover
the visible area of the list, we fire an `onFillRateExceeded` call with relevant stats for
logging the event through an analytics pipeline.

The measurement methodology is a little jank because everything is async, but it seems directionally
useful for getting ballpark numbers, catching regressions, and tracking improvements.

Benchmark testing shows a ~2014 MotoX starts hitting the fill rate limit at about 2500 px / sec,
which is pretty fast scrolling.

This also reworks our frame rate stuff so we can use a shared `SceneTracking` thing and track blankness
globally.

Reviewed By: bvaughn

Differential Revision: D4806867

fbshipit-source-id: 119bf177463c8c3aa51fa13d1a9d03b1a96042aa

Libraries/ReactNative/AppRegistry.js

@@ -16,6 +16,7 @@ const BugReporting = require('BugReporting');
 const FrameRateLogger = require('FrameRateLogger');
 const NativeModules = require('NativeModules');
 const ReactNative = require('ReactNative');
+const SceneTracker = require('SceneTracker');
 
 const infoLog = require('infoLog');
 const invariant = require('fbjs/lib/invariant');
@@ -56,6 +57,8 @@ const sections: Runnables = {};
 const tasks: Map<string, TaskProvider> = new Map();
 let componentProviderInstrumentationHook: ComponentProviderInstrumentationHook =
   (component: ComponentProvider) => component();
+let _frameRateLoggerSceneListener = null;
+
 
 /**
  * `AppRegistry` is the JS entry point to running all React Native apps.  App
@@ -173,7 +176,12 @@ const AppRegistry = {
       'This error can also happen due to a require() error during ' +
       'initialization or failure to call AppRegistry.registerComponent.\n\n'
     );
-    FrameRateLogger.setContext(appKey);
+    if (!_frameRateLoggerSceneListener) {
+      _frameRateLoggerSceneListener = SceneTracker.addActiveSceneChangedListener(
+        (scene) => FrameRateLogger.setContext(scene.name)
+      );
+    }
+    SceneTracker.setActiveScene({name: appKey});
     runnables[appKey].run(appParameters);
   },