Add PaintOptimizations feature to control subsequence caching and empty phase skipping

third_party/WebKit/Source/core/paint/PaintLayerPainter.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 "core/paint/PaintLayerPainter.h"
 
 #include "core/frame/FrameView.h"
 #include "core/frame/Settings.h"
 #include "core/layout/ClipPathOperation.h"
 #include "core/layout/LayoutBlock.h"
@@ skipping 167 matching lines @@
 private:
     LayoutSVGResourceClipper* m_resourceClipper;
     Optional<ClipPathRecorder> m_clipPathRecorder;
     SVGClipPainter::ClipperState m_clipperState;
     const PaintLayer& m_paintLayer;
     GraphicsContext& m_context;
 };
 
 static bool shouldCreateSubsequence(const PaintLayer& paintLayer, GraphicsContext& context, const PaintLayerPaintingInfo& paintingInfo, PaintLayerFlags paintFlags)
 {
+    if (!RuntimeEnabledFeatures::paintOptimizationsEnabled())
+        return false;
+
     // Caching is not needed during printing.
     if (context.printing())
         return false;
 
     // Don't create subsequence for a composited layer because if it can be cached,
     // we can skip the whole painting in GraphicsLayer::paint() with CachedDisplayItemList.
     // This also avoids conflict of PaintLayer::previousXXX() when paintLayer is composited
     // scrolling and is painted twice for GraphicsLayers of container and scrolling contents.
     if (paintLayer.compositingState() == PaintsIntoOwnBacking)
         return false;
@@ skipping 534 matching lines @@
     if (shouldClip && needsToClip(localPaintingInfo, layerFragments[0].foregroundRect)) {
         clipRecorder.emplace(context, *m_paintLayer.layoutObject(), DisplayItem::ClipLayerForeground, layerFragments[0].foregroundRect, &localPaintingInfo, layerFragments[0].paginationOffset, paintFlags);
         clipState = HasClipped;
     }
 
     // We have to loop through every fragment multiple times, since we have to issue paint invalidations in each specific phase in order for
     // interleaving of the fragments to work properly.
     if (selectionOnly) {
         paintForegroundForFragmentsWithPhase(PaintPhaseSelection, layerFragments, context, localPaintingInfo, paintFlags, clipState);
     } else {
-        if (m_paintLayer.needsPaintPhaseDescendantBlockBackgrounds())
+        if (!RuntimeEnabledFeatures::paintOptimizationsEnabled() || m_paintLayer.needsPaintPhaseDescendantBlockBackgrounds())
             paintForegroundForFragmentsWithPhase(PaintPhaseDescendantBlockBackgroundsOnly, layerFragments, context, localPaintingInfo, paintFlags, clipState);
-        if (m_paintLayer.needsPaintPhaseFloat())
+        if (!RuntimeEnabledFeatures::paintOptimizationsEnabled() || m_paintLayer.needsPaintPhaseFloat())
             paintForegroundForFragmentsWithPhase(PaintPhaseFloat, layerFragments, context, localPaintingInfo, paintFlags, clipState);
         paintForegroundForFragmentsWithPhase(PaintPhaseForeground, layerFragments, context, localPaintingInfo, paintFlags, clipState);
-        if (m_paintLayer.needsPaintPhaseDescendantOutlines())
+        if (!RuntimeEnabledFeatures::paintOptimizationsEnabled() || m_paintLayer.needsPaintPhaseDescendantOutlines())
             paintForegroundForFragmentsWithPhase(PaintPhaseDescendantOutlinesOnly, layerFragments, context, localPaintingInfo, paintFlags, clipState);
     }
 }
 
 void PaintLayerPainter::paintForegroundForFragmentsWithPhase(PaintPhase phase,
     const PaintLayerFragments& layerFragments, GraphicsContext& context,
     const PaintLayerPaintingInfo& localPaintingInfo, PaintLayerFlags paintFlags, ClipState clipState)
 {
     bool needsScope = layerFragments.size() > 1;
     for (auto& fragment : layerFragments) {
@@ skipping 49 matching lines @@
     if (!m_paintLayer.containsDirtyOverlayScrollbars())
         return;
 
     PaintLayerPaintingInfo paintingInfo(&m_paintLayer, LayoutRect(enclosingIntRect(damageRect)), paintFlags, LayoutSize());
     paintLayer(context, paintingInfo, PaintLayerPaintingOverlayScrollbars);
 
     m_paintLayer.setContainsDirtyOverlayScrollbars(false);
 }
 
 } // namespace blink