Skip paint chunks with effectively invisible opacity.

third_party/WebKit/Source/core/paint/PaintLayer.cpp

Index: third_party/WebKit/Source/core/paint/PaintLayer.cpp
diff --git a/third_party/WebKit/Source/core/paint/PaintLayer.cpp b/third_party/WebKit/Source/core/paint/PaintLayer.cpp
index 7100c617d45d4d9dd7ab901aaf3503bd6d934b02..738fdab1f6dd4cd203fb33efd7d26b34d9d891a8 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayer.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintLayer.cpp
@@ -2766,6 +2766,33 @@ bool PaintLayer::SupportsSubsequenceCaching() const {
   return true;
 }
 
+bool PaintLayer::IsComposited() const {

[wkorman, 2017/04/20 22:23:56]

There is other logic in PaintLayer that checks GetCompositingState() and that
perhaps we'd want to follow this method instead, but I thought best to keep this
change focused on this one spot.

I also considered adding a HasDirectCompositingReasons() method to
ObjectPaintProperties to encapsulate the below but OPP is a very simple data
model currently and so I hesitated to add such logic there for currently just
this one call site, but open to thought.

+  if (RuntimeEnabledFeatures::slimmingPaintV2Enabled()) {
+    // In SPv2 paint layers always have a compositing state of
+    // kNotComposited. We instead determine compositing state by checking for a
+    // direct compositing reason on either the transform or effect node.
+    const ObjectPaintProperties* properties =
+        GetLayoutObject().PaintProperties();
+    if (!properties)
+      return false;
+    const TransformPaintPropertyNode* transform = properties->Transform();
+    if (transform && transform->HasDirectCompositingReasons())
+      return true;
+    const EffectPaintPropertyNode* effect = properties->Effect();
+    if (effect && effect->HasDirectCompositingReasons())
+      return true;
+    return false;
+  }
+  return GetCompositingState() == kPaintsIntoOwnBacking;
+}
+
+bool PaintLayer::PaintsWithTransparency(
+    GlobalPaintFlags global_paint_flags) const {
+  return IsTransparent() &&
+         ((global_paint_flags & kGlobalPaintFlattenCompositingLayers) ||
+          !IsComposited());
+}
+
 ScrollingCoordinator* PaintLayer::GetScrollingCoordinator() {
   Page* page = GetLayoutObject().GetFrame()->GetPage();
   return (!page) ? nullptr : page->GetScrollingCoordinator();