Add PaintOptimizations feature to control subsequence caching and empty phase skipping

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 337de3731f19143e51e1e61cea3e9036a38fd40d..f51fa53d6145dac05305a8bc7228f910c1ef27e3 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayerPainter.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintLayerPainter.cpp
@@ -185,6 +185,9 @@ private:
 
 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;
@@ -739,12 +742,12 @@ void PaintLayerPainter::paintForegroundForFragments(const PaintLayerFragments& l
     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);
     }
 }