Add a new top-level inspector timeline event for the PrePaint step

third_party/WebKit/Source/devtools/front_end/timeline_model/TimelineModel.js

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 1152 matching lines @@
   ActivateLayerTree: 'ActivateLayerTree',
   DrawFrame: 'DrawFrame',
   HitTest: 'HitTest',
   ScheduleStyleRecalculation: 'ScheduleStyleRecalculation',
   RecalculateStyles: 'RecalculateStyles',  // For backwards compatibility only, now replaced by UpdateLayoutTree.
   UpdateLayoutTree: 'UpdateLayoutTree',
   InvalidateLayout: 'InvalidateLayout',
   Layout: 'Layout',
   UpdateLayer: 'UpdateLayer',
   UpdateLayerTree: 'UpdateLayerTree',
+  PreparePaint: 'PreparePaint',
   PaintSetup: 'PaintSetup',
   Paint: 'Paint',
   PaintImage: 'PaintImage',
   Rasterize: 'Rasterize',
   RasterTask: 'RasterTask',
   ScrollLayer: 'ScrollLayer',
   CompositeLayers: 'CompositeLayers',
 
   ScheduleStyleInvalidationTracking: 'ScheduleStyleInvalidationTracking',
   StyleRecalcInvalidationTracking: 'StyleRecalcInvalidationTracking',
@@ skipping 870 matching lines @@
     var data = event[TimelineModel.TimelineData._symbol];
     if (!data) {
       data = new TimelineModel.TimelineData();
       event[TimelineModel.TimelineData._symbol] = data;
     }
     return data;
   }
 };
 
 TimelineModel.TimelineData._symbol = Symbol('timelineData');