ImageQualityController should not post hundreds of canceled tasks.

third_party/WebKit/Source/core/layout/ImageQualityController.cpp

 /*
  * Copyright (C) 2013 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 124 matching lines @@
             continue;
 
         // TODO(wangxianzhu): Use LayoutObject::getMutableForPainting().
         const_cast<LayoutObject*>(i.key)->setShouldDoFullPaintInvalidation();
         i.value.isResizing = false;
     }
 }
 
 void ImageQualityController::restartTimer()
 {
-    m_timer->startOneShot(cLowQualityTimeThreshold, BLINK_FROM_HERE);
+    // Avoid reposting the timer if it's already active. While it does cancel

[chrishtr, 2016/04/21 20:30:59]

restartTimer() is called in order to push the 500ms period forward. If you don't
call it, then after 500ms of continuous animation the timer will expire,
at which point a high-quality resize will happen. Instead I think something is
needed to only push it forward if most of the time of the timer has expired.

+    // the previous one, the MessageLoop does not actually support cancelation
+    // which means on a page with hundreds of images we end up processing
+    // hundreds of cancelled tasks.
+    if (!m_timer->isActive())
+        m_timer->startOneShot(cLowQualityTimeThreshold, BLINK_FROM_HERE);
 }
 
 bool ImageQualityController::shouldPaintAtLowQuality(const LayoutObject& object, Image* image, const void *layer, const LayoutSize& layoutSize)
 {
     // If the image is not a bitmap image, then none of this is relevant and we just paint at high
     // quality.
     if (!image || !image->isBitmapImage())
         return false;
 
     if (!layer)
@@ skipping 50 matching lines @@
     }
     // This object has been resized to two different sizes while the timer
     // is active, so draw at low quality, set the flag for animated resizes and
     // the object to the list for high quality redraw.
     set(object, innerMap, layer, layoutSize, true);
     restartTimer();
     return true;
 }
 
 } // namespace blink