ImageQualityController should not post hundreds of canceled tasks.

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

Index: third_party/WebKit/Source/core/layout/ImageQualityController.cpp
diff --git a/third_party/WebKit/Source/core/layout/ImageQualityController.cpp b/third_party/WebKit/Source/core/layout/ImageQualityController.cpp
index c9ef4c3fb973653d65d7e64b3b328bafb1085180..9b4923996e82540fab0e2df2ff72370a019a2b89 100644
--- a/third_party/WebKit/Source/core/layout/ImageQualityController.cpp
+++ b/third_party/WebKit/Source/core/layout/ImageQualityController.cpp
@@ -142,7 +142,12 @@ void ImageQualityController::highQualityRepaintTimerFired(Timer<ImageQualityCont
 
 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)