Add more specific metrics for main thread scrolling reasons

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

 /*
  * Copyright (C) 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2014 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 10 matching lines @@
  * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
  * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #include "core/layout/compositing/CompositingRequirementsUpdater.h"
 
 #include "core/layout/LayoutView.h"
 #include "core/layout/compositing/PaintLayerCompositor.h"
+#include "core/page/Page.h"
+#include "core/page/scrolling/ScrollingCoordinator.h"
 #include "core/paint/PaintLayer.h"
 #include "core/paint/PaintLayerStackingNode.h"
 #include "core/paint/PaintLayerStackingNodeIterator.h"
 #include "platform/tracing/TraceEvent.h"
 
 namespace blink {
 
 class OverlapMapContainer {
  public:
   void add(const IntRect& bounds) {
@@ skipping 202 matching lines @@
     Vector<PaintLayer*>& unclippedDescendants,
     IntRect& absoluteDescendantBoundingBox) {
   PaintLayerCompositor* compositor = m_layoutView.compositor();
 
   layer->stackingNode()->updateLayerListsIfNeeded();
 
   CompositingReasons reasonsToComposite = CompositingReasonNone;
   CompositingReasons directReasons =
       m_compositingReasonFinder.directReasons(layer);
 
+  updateMainThreadScrollingReasonsFromStyle(layer);
+
   // Video is special. It's the only PaintLayer type that can both have
   // PaintLayer children and whose children can't use its backing to render
   // into. These children (the controls) always need to be promoted into their
   // own layers to draw on top of the accelerated video.
   if (currentRecursionData.m_compositingAncestor &&
       currentRecursionData.m_compositingAncestor->layoutObject()->isVideo())
     directReasons |= CompositingReasonVideoOverlay;
 
   bool hasCompositedScrollingAncestor =
       layer->ancestorScrollingLayer() &&
@@ skipping 274 matching lines @@
 
     descendantHas3DTransform |=
         anyDescendantHas3DTransform || layer->has3DTransform();
   }
 
   // At this point we have finished collecting all reasons to composite this
   // layer.
   layer->setCompositingReasons(reasonsToComposite);
 }
 
+// Check if current layer has layout object that contains properties that cause
+// main thread scrolling.
+void CompositingRequirementsUpdater::updateMainThreadScrollingReasonsFromStyle(
+    const PaintLayer* layer) const {
+  // If current layer has opacity and has not been recorded, add the layer into
+  // frameView and vice versa.
+  if (!layer || !layer->getScrollableArea())
+    return;
+  if (layer->compositesWithOpacity() !=
+      layer->getScrollableArea()->hasMainThreadScrollingReason(
+          MainThreadScrollingReason::kHasOpacity)) {
+    layer->getScrollableArea()->flipMainThreadScrollingReason(
+        MainThreadScrollingReason::kHasOpacity);
+
+    if (ScrollingCoordinator* scrollingCoordinator =

[bokan, 2016/12/15 20:47:45]

Should we early out above if there's no scrolling coordinator? Seems like we
shouldn't set the scrolling reason on the PaintLayer unless we do it on the
ScrollingCoordinator too (otherwise if we add one after they'll be out of sync)

[yigu, 2016/12/16 18:17:39]

Done.

+            m_layoutView.document().page()->scrollingCoordinator()) {
+      scrollingCoordinator->adjustMainThreadReasonsFromStyle(
+          MainThreadScrollingReason::kHasOpacity,
+          layer->compositesWithOpacity());
+    }
+  }
+}
+
 }  // namespace blink