Skip PaintLayer empty paint phases if it previously painted nothing

third_party/WebKit/Source/core/layout/LayoutBox.cpp

Index: third_party/WebKit/Source/core/layout/LayoutBox.cpp
diff --git a/third_party/WebKit/Source/core/layout/LayoutBox.cpp b/third_party/WebKit/Source/core/layout/LayoutBox.cpp
index c48220c9b982670f937e3d025d61a06373815254..35f75a72a61146a7cab3d8efc29ee8ea6ef17103 100644
--- a/third_party/WebKit/Source/core/layout/LayoutBox.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutBox.cpp
@@ -1482,15 +1482,15 @@ bool LayoutBox::intersectsVisibleViewport()
 
 PaintInvalidationReason LayoutBox::invalidatePaintIfNeeded(PaintInvalidationState& paintInvalidationState, const LayoutBoxModelObject& paintInvalidationContainer)
 {
-    if (isFloating())
-        paintInvalidationState.enclosingSelfPaintingLayer(*this).setNeedsPaintPhaseFloat();
-
-    if (hasBoxDecorationBackground()
-        // We also paint overflow controls in background phase.
-        || (hasOverflowClip() && scrollableArea()->hasOverflowControls())) {
-        PaintLayer& layer = paintInvalidationState.enclosingSelfPaintingLayer(*this);
-        if (layer.layoutObject() != this)
-            layer.setNeedsPaintPhaseDescendantBlockBackgrounds();
+    PaintLayer& enclosingSelfPaintingLayer = paintInvalidationState.enclosingSelfPaintingLayer(*this);
+    if (enclosingSelfPaintingLayer.layoutObject() != this) {
+        if (isFloating())
+            enclosingSelfPaintingLayer.setNeedsPaintPhaseFloat();

[Xianzhu, 2016/03/08 22:08:42]

This change is because a self-painting floating layer just paints its contents
normally, not needing PaintPhaseFloat by itself.

+
+        if (hasBoxDecorationBackground()
+            // We also paint overflow controls in background phase.
+            || (hasOverflowClip() && scrollableArea()->hasOverflowControls()))
+            enclosingSelfPaintingLayer.setNeedsPaintPhaseDescendantBlockBackgrounds();

[chrishtr, 2016/03/09 03:40:47]

A self-painting layer also doesn't need PaintPhaseDescendantBlockBackgrounds?

[Xianzhu, 2016/03/09 21:39:52]

Right. The layer paints its own background in PaintPhaseSelfBlockBackgroundOnly.

     }
 
     PaintInvalidationReason fullInvalidationReason = fullPaintInvalidationReason();