Restart any animations when we allocate a composited layer.

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

 /*
  * Copyright (C) 1998, 1999 Torben Weis <weis@kde.org>
  *                     1999 Lars Knoll <knoll@kde.org>
  *                     1999 Antti Koivisto <koivisto@kde.org>
  *                     2000 Dirk Mueller <mueller@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007, 2008 Apple Inc. All rights reserved.
  *           (C) 2006 Graham Dennis (graham.dennis@gmail.com)
  *           (C) 2006 Alexey Proskuryakov (ap@nypop.com)
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
@@ skipping 3839 matching lines @@
 }
 
 IntPoint FrameView::convertFromContainingWidgetToScrollbar(const Scrollbar& scrollbar, const IntPoint& parentPoint) const
 {
     IntPoint newPoint = parentPoint;
     // Scrollbars won't be transformed within us
     newPoint.moveBy(-scrollbar.location());
     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);
 
     if (!isSelfVisible())
         return;
 
     for (const auto& child : m_children)
         child->setParentVisible(visible);
 }
 
 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)
                 child->setParentVisible(true);
         }
     }
 
     Widget::show();
 }
 
 void FrameView::hide()
 {
     if (isSelfVisible()) {
         if (isParentVisible()) {
             for (const auto& child : m_children)
                 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();
     }
 
     Widget::hide();
 }
 
 int FrameView::viewportWidth() const
 {
     int viewportWidth = layoutSize(IncludeScrollbars).width();
     return adjustForAbsoluteZoom(viewportWidth, layoutView());
@@ skipping 197 matching lines @@
     return m_subtreeThrottled || (m_hiddenForThrottling && m_crossOriginForThrottling);
 }
 
 LayoutBox& FrameView::boxForScrollControlPaintInvalidation() const
 {
     ASSERT(layoutView());
     return *layoutView();
 }
 
 } // namespace blink