Fix a race condition in canvas hibernation when visibility is toggled repeatedly

third_party/WebKit/Source/platform/graphics/Canvas2DLayerBridge.cpp

Index: third_party/WebKit/Source/platform/graphics/Canvas2DLayerBridge.cpp
diff --git a/third_party/WebKit/Source/platform/graphics/Canvas2DLayerBridge.cpp b/third_party/WebKit/Source/platform/graphics/Canvas2DLayerBridge.cpp
index 49a2d787ddd0905f4d6ca69cbd9aded38fa7b9a5..25df12691278e2dc1a0ef8e332c9130e38e93924 100644
--- a/third_party/WebKit/Source/platform/graphics/Canvas2DLayerBridge.cpp
+++ b/third_party/WebKit/Source/platform/graphics/Canvas2DLayerBridge.cpp
@@ -207,6 +207,9 @@ static void hibernateWrapper(WeakPtr<Canvas2DLayerBridge> bridge, double /*idleD
 void Canvas2DLayerBridge::hibernate()
 {
     ASSERT(!isHibernating());
+    ASSERT(m_hibernationScheduled);
+
+    m_hibernationScheduled = false;

[Stephen White, 2016/02/26 20:16:04]

For the future, it might be worth thinking about turning Canvas2DLayerBridge
into a state machine, and turning (some of) these bools into an enum.

 
     if (m_destructionInProgress) {
         m_logger->reportHibernationEvent(HibernationAbortedDueToPendingDestruction);
@@ -421,10 +424,11 @@ void Canvas2DLayerBridge::setIsHidden(bool hidden)
         return;
 
     m_isHidden = newHiddenValue;
-    if (m_surface && isHidden() && !m_destructionInProgress) {
+    if (m_surface && isHidden() && !m_destructionInProgress && !m_hibernationScheduled) {
         if (m_layer)
             m_layer->clearTexture();
         m_logger->reportHibernationEvent(HibernationScheduled);
+        m_hibernationScheduled = true;
         Platform::current()->currentThread()->scheduler()->postIdleTask(BLINK_FROM_HERE, WTF::bind<double>(&hibernateWrapper, m_weakPtrFactory.createWeakPtr()));
     }
     if (!isHidden() && m_softwareRenderingWhileHidden) {