Restart any animations when we allocate a composited layer.

third_party/WebKit/Source/core/layout/compositing/PaintLayerCompositor.cpp

Index: third_party/WebKit/Source/core/layout/compositing/PaintLayerCompositor.cpp
diff --git a/third_party/WebKit/Source/core/layout/compositing/PaintLayerCompositor.cpp b/third_party/WebKit/Source/core/layout/compositing/PaintLayerCompositor.cpp
index 3f2989fa7c51c0b6cdee51c7037f4a815a8b0db6..58a1ff7a906827e2aca5ae432dd0daef1d512b24 100644
--- a/third_party/WebKit/Source/core/layout/compositing/PaintLayerCompositor.cpp
+++ b/third_party/WebKit/Source/core/layout/compositing/PaintLayerCompositor.cpp
@@ -27,6 +27,7 @@
 
 #include "core/animation/AnimationTimeline.h"
 #include "core/animation/DocumentAnimations.h"
+#include "core/animation/ElementAnimations.h"
 #include "core/dom/DOMNodeIds.h"
 #include "core/dom/Fullscreen.h"
 #include "core/editing/FrameSelection.h"
@@ -457,6 +458,14 @@ void PaintLayerCompositor::updateIfNeeded()
         InspectorInstrumentation::layerTreeDidChange(m_layoutView.frame());
 }
 
+static void restartAnimationOnCompositor(const LayoutObject& layoutObject)
+{
+    Node* node = layoutObject.node();
+    ElementAnimations* elementAnimations = (node && node->isElementNode()) ? toElement(node)->elementAnimations() : nullptr;
+    if (elementAnimations)
+        elementAnimations->restartAnimationOnCompositor();
+}
+
 bool PaintLayerCompositor::allocateOrClearCompositedLayerMapping(PaintLayer* layer, const CompositingStateTransitionType compositedLayerUpdate)
 {
     bool compositedLayerMappingChanged = false;
@@ -483,7 +492,9 @@ bool PaintLayerCompositor::allocateOrClearCompositedLayerMapping(PaintLayer* lay
         layer->ensureCompositedLayerMapping();
         compositedLayerMappingChanged = true;
 
-        // At this time, the ScrollingCooridnator only supports the top-level frame.
+        restartAnimationOnCompositor(*layer->layoutObject());

[chrishtr, 2016/05/28 21:18:22]

One thing I'd like to understand: in the scenario of a composited animation
where
in the middle of it, will-change: transform is removed and then added again,
does the animation start running on the compositor again? If so, what makes it
do
so in the code before this CL?

[ajuma, 2016/05/29 00:49:28]

Having a transform animation is a direct compositing reason, so adding/removing
will-change in the middle has no effect (the composited layer persists for the
duration of the animation). The case this CL is trying to handle is unusual: the
layer has a direct compositing reason (the animation), but we're still choosing
to stop compositing it because it's inside an invisible frame.

+
+        // At this time, the ScrollingCoordinator only supports the top-level frame.
         if (layer->isRootLayer() && m_layoutView.frame()->isLocalRoot()) {
             if (ScrollingCoordinator* scrollingCoordinator = this->scrollingCoordinator())
                 scrollingCoordinator->frameViewRootLayerDidChange(m_layoutView.frameView());