Restart any animations when we allocate a composited layer.

third_party/WebKit/Source/core/frame/FrameView.cpp

Index: third_party/WebKit/Source/core/frame/FrameView.cpp
diff --git a/third_party/WebKit/Source/core/frame/FrameView.cpp b/third_party/WebKit/Source/core/frame/FrameView.cpp
index 3b83f9284b89e7d5a525dd57a3ddcc42399abf42..745035dcc59b9c5fb7aaa7bc7662dac8d3aa40f1 100644
--- a/third_party/WebKit/Source/core/frame/FrameView.cpp
+++ b/third_party/WebKit/Source/core/frame/FrameView.cpp
@@ -3857,14 +3857,19 @@ IntPoint FrameView::convertFromContainingWidgetToScrollbar(const Scrollbar& scro
     return newPoint;
 }
 
+static void setNeedsCompositingUpdate(LayoutViewItem layoutViewItem, CompositingUpdateType updateType)
+{
+    if (PaintLayerCompositor* compositor = !layoutViewItem.isNull() ? layoutViewItem.compositor() : nullptr)
+        compositor->setNeedsCompositingUpdate(updateType);
+}
+
 void FrameView::setParentVisible(bool visible)
 {
     if (isParentVisible() == visible)
         return;
 
     // As parent visibility changes, we may need to recomposite this frame view and potentially child frame views.
-    if (PaintLayerCompositor* compositor = !layoutViewItem().isNull() ? layoutViewItem().compositor() : nullptr)
-        compositor->setNeedsCompositingUpdate(CompositingUpdateRebuildTree);
+    setNeedsCompositingUpdate(layoutViewItem(), CompositingUpdateRebuildTree);
 
     Widget::setParentVisible(visible);
 
@@ -3879,6 +3884,7 @@ void FrameView::show()
 {
     if (!isSelfVisible()) {
         setSelfVisible(true);
+        setNeedsCompositingUpdate(layoutViewItem(), CompositingUpdateRebuildTree);

[wkorman, 2016/05/28 00:59:44]

As an alternative to adding this here and in line 3906 below, we could override
Widget::setSelfVisible() and then we could do this, and updateScrollableAreaSet,
in there. Should be equivalent. I sort of prefer not overriding things since
perhaps we don't always want to do these two operations, but I can be convinced.
Note we do already override Widget::setParentVisible() above.

         updateScrollableAreaSet();
         if (isParentVisible()) {
             for (const auto& child : m_children)
@@ -3897,6 +3903,7 @@ void FrameView::hide()
                 child->setParentVisible(false);
         }
         setSelfVisible(false);
+        setNeedsCompositingUpdate(layoutViewItem(), CompositingUpdateRebuildTree);

[wkorman, 2016/05/28 00:59:44]

This is not needed to fix the bug, but it maintains symmetry with show() and I
believe that without this a composited iframe subsequently hidden won't have its
then-unneeded layer removed until something else causes a lifecycle update
through to compositing clean.

         updateScrollableAreaSet();
     }