Enable fast/images with slimming paint

Source/core/paint/BoxPainter.cpp

Index: Source/core/paint/BoxPainter.cpp
diff --git a/Source/core/paint/BoxPainter.cpp b/Source/core/paint/BoxPainter.cpp
index 152cb6cc691fe1f2aec53d1e0f06ff40e6458c91..99926941043325b46783c8d48194132fb2eb90e7 100644
--- a/Source/core/paint/BoxPainter.cpp
+++ b/Source/core/paint/BoxPainter.cpp
@@ -11,6 +11,7 @@
 #include "core/paint/BackgroundImageGeometry.h"
 #include "core/paint/BoxDecorationData.h"
 #include "core/paint/DrawingRecorder.h"
+#include "core/paint/TransparencyDisplayItem.h"
 #include "core/rendering/ImageQualityController.h"
 #include "core/rendering/PaintInfo.h"
 #include "core/rendering/RenderBox.h"
@@ -515,7 +516,7 @@ void BoxPainter::paintMask(const PaintInfo& paintInfo, const LayoutPoint& paintO
 void BoxPainter::paintMaskImages(const PaintInfo& paintInfo, const LayoutRect& paintRect)
 {
     // Figure out if we need to push a transparency layer to render our mask.
-    bool pushTransparencyLayer = false;
+    OwnPtr<TransparencyRecorder> transparencyRecorder;
     bool compositedMask = m_renderBox.hasLayer() && m_renderBox.layer()->hasCompositedMask();
     bool flattenCompositingLayers = m_renderBox.view()->frameView() && m_renderBox.view()->frameView()->paintBehavior() & PaintBehaviorFlattenCompositingLayers;
     CompositeOperator compositeOp = CompositeSourceOver;
@@ -523,7 +524,6 @@ void BoxPainter::paintMaskImages(const PaintInfo& paintInfo, const LayoutRect& p
     bool allMaskImagesLoaded = true;
 
     if (!compositedMask || flattenCompositingLayers) {
-        pushTransparencyLayer = true;
         StyleImage* maskBoxImage = m_renderBox.style()->maskBoxImage().image();
         const FillLayer& maskLayers = m_renderBox.style()->maskLayers();
 
@@ -534,7 +534,9 @@ void BoxPainter::paintMaskImages(const PaintInfo& paintInfo, const LayoutRect& p
         allMaskImagesLoaded &= maskLayers.imagesAreLoaded();
 
         paintInfo.context->setCompositeOperation(CompositeDestinationIn);
-        paintInfo.context->beginTransparencyLayer(1);
+
+        transparencyRecorder = adoptPtr(new TransparencyRecorder(paintInfo.context, &m_renderBox, DisplayItem::BeginTransparency, WebBlendModeNormal, 1));

[chrishtr, 2014/11/26 17:20:59]

On reflection, I think this was maybe wrong. The only reason to store separate
transparency display items is to separate pieces of painted state from the
current render object and its children, or if the transparency is a compositing
trigger. I don't think either is true in this case. Instead, we should allocate
a DrawingRecorder for the mask phase, in BoxPainter::paintMask(). I'm trying
this approach now.

+
         compositeOp = CompositeSourceOver;
     }
 
@@ -542,9 +544,6 @@ void BoxPainter::paintMaskImages(const PaintInfo& paintInfo, const LayoutRect& p
         paintFillLayers(paintInfo, Color::transparent, m_renderBox.style()->maskLayers(), paintRect, BackgroundBleedNone, compositeOp);
         paintNinePieceImage(m_renderBox, paintInfo.context, paintRect, m_renderBox.style(), m_renderBox.style()->maskBoxImage(), compositeOp);
     }
-
-    if (pushTransparencyLayer)
-        paintInfo.context->endLayer();
 }
 
 void BoxPainter::paintClippingMask(const PaintInfo& paintInfo, const LayoutPoint& paintOffset)