Skip PaintLayer empty paint phases if it previously painted nothing

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

Index: third_party/WebKit/Source/core/paint/PaintLayerPainter.cpp
diff --git a/third_party/WebKit/Source/core/paint/PaintLayerPainter.cpp b/third_party/WebKit/Source/core/paint/PaintLayerPainter.cpp
index 1dd3743352d2028eda0ef7f14961428a9535a298..e717da6a3e707d4d98f08ae8b9745a76730ca0af 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayerPainter.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintLayerPainter.cpp
@@ -215,6 +215,7 @@ static bool shouldCreateSubsequence(const PaintLayer& paintLayer, GraphicsContex
 static bool shouldRepaintSubsequence(PaintLayer& paintLayer, const PaintLayerPaintingInfo& paintingInfo, ShouldRespectOverflowClipType respectOverflowClip, const LayoutSize& subpixelAccumulation)
 {
     bool needsRepaint = false;
+    bool needsResetEmptyPaintPhaseFlags = false;
 
     // Repaint subsequence if the layer is marked for needing repaint.
     if (paintLayer.needsRepaint())
@@ -223,20 +224,32 @@ static bool shouldRepaintSubsequence(PaintLayer& paintLayer, const PaintLayerPai
     // Repaint if layer's clip changes.
     ClipRects& clipRects = paintLayer.clipper().paintingClipRects(paintingInfo.rootLayer, respectOverflowClip, subpixelAccumulation);
     ClipRects* previousClipRects = paintLayer.previousPaintingClipRects();
-    if (!needsRepaint && &clipRects != previousClipRects && (!previousClipRects || clipRects != *previousClipRects))
+    if (&clipRects != previousClipRects && (!previousClipRects || clipRects != *previousClipRects)) {
         needsRepaint = true;
+        needsResetEmptyPaintPhaseFlags = true;
+    }
     paintLayer.setPreviousPaintingClipRects(clipRects);
 
     // Repaint if previously the layer might be clipped by paintDirtyRect and paintDirtyRect changes.
-    if (!needsRepaint && paintLayer.previousPaintResult() == PaintLayerPainter::MayBeClippedByPaintDirtyRect && paintLayer.previousPaintDirtyRect() != paintingInfo.paintDirtyRect)
+    if (paintLayer.previousPaintResult() == PaintLayerPainter::MayBeClippedByPaintDirtyRect && paintLayer.previousPaintDirtyRect() != paintingInfo.paintDirtyRect) {
         needsRepaint = true;
+        needsResetEmptyPaintPhaseFlags = true;
+    }
     paintLayer.setPreviousPaintDirtyRect(paintingInfo.paintDirtyRect);
 
     // Repaint if scroll offset accumulation changes.
-    if (!needsRepaint && paintingInfo.scrollOffsetAccumulation != paintLayer.previousScrollOffsetAccumulationForPainting())
+    if (paintingInfo.scrollOffsetAccumulation != paintLayer.previousScrollOffsetAccumulationForPainting()) {
         needsRepaint = true;
+        needsResetEmptyPaintPhaseFlags = true;
+    }
     paintLayer.setPreviousScrollOffsetAccumulationForPainting(paintingInfo.scrollOffsetAccumulation);
 
+    if (needsResetEmptyPaintPhaseFlags) {
+        paintLayer.setPreviousPaintPhaseDescendantOutlinesEmpty(false);
+        paintLayer.setPreviousPaintPhaseFloatEmpty(false);
+        paintLayer.setPreviousPaintPhaseDescendantBlockBackgroundsEmpty(false);
+    }
+
     return needsRepaint;
 }
 
@@ -699,13 +712,22 @@ void PaintLayerPainter::paintForegroundForFragments(const PaintLayerFragments& l
     if (selectionOnly) {
         paintForegroundForFragmentsWithPhase(PaintPhaseSelection, layerFragments, context, localPaintingInfo, paintFlags, clipState);
     } else {
-        if (m_paintLayer.needsPaintPhaseDescendantBlockBackgrounds())
+        if (m_paintLayer.needsPaintPhaseDescendantBlockBackgrounds()) {
+            size_t sizeBefore = context.paintController().newDisplayItemList().size();
             paintForegroundForFragmentsWithPhase(PaintPhaseDescendantBlockBackgroundsOnly, layerFragments, context, localPaintingInfo, paintFlags, clipState);
-        if (m_paintLayer.needsPaintPhaseFloat())
+            m_paintLayer.setPreviousPaintPhaseDescendantBlockBackgroundsEmpty(context.paintController().newDisplayItemList().size() == sizeBefore);
+        }
+        if (m_paintLayer.needsPaintPhaseFloat()) {
+            size_t sizeBefore = context.paintController().newDisplayItemList().size();
             paintForegroundForFragmentsWithPhase(PaintPhaseFloat, layerFragments, context, localPaintingInfo, paintFlags, clipState);
+            m_paintLayer.setPreviousPaintPhaseFloatEmpty(context.paintController().newDisplayItemList().size() == sizeBefore);
+        }
         paintForegroundForFragmentsWithPhase(PaintPhaseForeground, layerFragments, context, localPaintingInfo, paintFlags, clipState);
-        if (m_paintLayer.needsPaintPhaseDescendantOutlines())
+        if (m_paintLayer.needsPaintPhaseDescendantOutlines()) {
+            size_t sizeBefore = context.paintController().newDisplayItemList().size();
             paintForegroundForFragmentsWithPhase(PaintPhaseDescendantOutlinesOnly, layerFragments, context, localPaintingInfo, paintFlags, clipState);
+            m_paintLayer.setPreviousPaintPhaseDescendantOutlinesEmpty(context.paintController().newDisplayItemList().size() == sizeBefore);
+        }
     }
 }