Implement will-change-based creation of layers, stacking contexts, and containing blocks

Source/core/rendering/compositing/CompositingReasonFinder.cpp

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "config.h"
 #include "core/rendering/compositing/CompositingReasonFinder.h"
 
 #include "CSSPropertyNames.h"
 #include "HTMLNames.h"
 #include "core/animation/ActiveAnimations.h"
@@ skipping 83 matching lines @@
 
     if (requiresCompositingForOverflowScrolling(layer))
         directReasons |= CompositingReasonOverflowScrollingTouch;
 
     if (requiresCompositingForOverflowScrollingParent(layer))
         directReasons |= CompositingReasonOverflowScrollingParent;
 
     if (requiresCompositingForOutOfFlowClipping(layer))
         directReasons |= CompositingReasonOutOfFlowClipping;
 
+    if (requiresCompositingForWillChange(renderer))
+        directReasons |= CompositingReasonWillChange;
+
     return directReasons;
 }
 
 bool CompositingReasonFinder::requiresCompositingForScrollableFrame() const
 {
     // Need this done first to determine overflow.
     ASSERT(!m_renderView.needsLayout());
     if (isMainFrame())
         return false;
 
@@ skipping 137 matching lines @@
 bool CompositingReasonFinder::requiresCompositingForOverflowScrollingParent(const RenderLayer* layer) const
 {
     return !!layer->scrollParent();
 }
 
 bool CompositingReasonFinder::requiresCompositingForOutOfFlowClipping(const RenderLayer* layer) const
 {
     return m_renderView.compositorDrivenAcceleratedScrollingEnabled() && layer->isUnclippedDescendant();
 }
 
+bool CompositingReasonFinder::requiresCompositingForWillChange(const RenderObject* renderer) const
+{
+    return renderer->style()->hasWillChangeCompositingHint();
+}
+
 bool CompositingReasonFinder::isViewportConstrainedFixedOrStickyLayer(const RenderLayer* layer)
 {
     if (layer->renderer()->isStickyPositioned())
         return !layer->enclosingOverflowClipLayer(ExcludeSelf);
 
     if (layer->renderer()->style()->position() != FixedPosition)
         return false;
 
     for (const RenderLayerStackingNode* stackingContainer = layer->stackingNode(); stackingContainer;
         stackingContainer = stackingContainer->ancestorStackingContainerNode()) {
@@ skipping 105 matching lines @@
 
     return true;
 }
 
 bool CompositingReasonFinder::requiresCompositingForOverflowScrolling(const RenderLayer* layer) const
 {
     return layer->needsCompositedScrolling();
 }
 
 }