Make GraphicsLayer the DisplayItemClient for scrollbars composited via PaintLayerCompositor.

third_party/WebKit/Source/core/layout/compositing/PaintLayerCompositor.cpp

Index: third_party/WebKit/Source/core/layout/compositing/PaintLayerCompositor.cpp
diff --git a/third_party/WebKit/Source/core/layout/compositing/PaintLayerCompositor.cpp b/third_party/WebKit/Source/core/layout/compositing/PaintLayerCompositor.cpp
index 26f74ec8bb84d91ae85a2125af480ac43b364989..6e24f93ee60cad417f8066a2a5d8fb37f55983c6 100644
--- a/third_party/WebKit/Source/core/layout/compositing/PaintLayerCompositor.cpp
+++ b/third_party/WebKit/Source/core/layout/compositing/PaintLayerCompositor.cpp
@@ -56,11 +56,13 @@
 #include "platform/RuntimeEnabledFeatures.h"
 #include "platform/ScriptForbiddenScope.h"
 #include "platform/TraceEvent.h"
+#include "platform/geometry/FloatRect.h"
 #include "platform/graphics/CompositorMutableProperties.h"
 #include "platform/graphics/GraphicsLayer.h"
 #include "platform/graphics/paint/CullRect.h"
 #include "platform/graphics/paint/DrawingRecorder.h"
 #include "platform/graphics/paint/PaintController.h"
+#include "platform/graphics/paint/SkPictureBuilder.h"
 #include "platform/graphics/paint/TransformDisplayItem.h"
 
 namespace blink {
@@ -791,21 +793,28 @@ bool PaintLayerCompositor::needsContentsCompositingLayer(const PaintLayer* layer
     return layer->stackingNode()->hasNegativeZOrderList();
 }
 
-static void paintScrollbar(const Scrollbar* scrollbar, GraphicsContext& context, const IntRect& clip)
+static void paintScrollbar(const GraphicsLayer* graphicsLayer, const Scrollbar* scrollbar, GraphicsContext& context, const IntRect& clip)
 {
     if (!scrollbar)
         return;
 
-    // Frame scrollbars are painted in the space of the containing frame, not the local space of the scrollbar.
-    const IntPoint& paintOffset = scrollbar->frameRect().location();
-    IntRect transformedClip = clip;
-    transformedClip.moveBy(paintOffset);
+    FloatRect layerBounds(FloatPoint(), graphicsLayer->size());
+    SkPictureBuilder pictureBuilder(layerBounds, nullptr, &context);

[chrishtr, 2016/03/22 19:45:47]

Factor the SkPictureBuilder into the calling function in order to:

- Fix the comment on line 832
- Avoid errors about choosing the correct GraphicsContext.

[wkorman, 2016/03/22 20:45:56]

Done.

 
-    AffineTransform translation;
-    translation.translate(-paintOffset.x(), -paintOffset.y());
-    TransformRecorder transformRecorder(context, *scrollbar, translation);
+    {
+        // Frame scrollbars are painted in the space of the containing frame, not the local space of the scrollbar.
+        const IntPoint& paintOffset = scrollbar->frameRect().location();
+        IntRect transformedClip = clip;
+        transformedClip.moveBy(paintOffset);
 
-    scrollbar->paint(context, CullRect(transformedClip));
+        AffineTransform translation;
+        translation.translate(-paintOffset.x(), -paintOffset.y());
+        TransformRecorder transformRecorder(pictureBuilder.context(), *scrollbar, translation);
+        scrollbar->paint(pictureBuilder.context(), CullRect(transformedClip));
+    }
+
+    DrawingRecorder drawingRecorder(context, *graphicsLayer, DisplayItem::ScrollbarCompositedScrollbar, layerBounds);
+    pictureBuilder.endRecording()->playback(context.canvas());

[chrishtr, 2016/03/22 19:45:47]

Add a comment about why there is replaying into a parent context.

[wkorman, 2016/03/22 20:45:56]

Done.

 }
 
 IntRect PaintLayerCompositor::computeInterestRect(const GraphicsLayer* graphicsLayer, const IntRect&) const
@@ -816,10 +825,11 @@ IntRect PaintLayerCompositor::computeInterestRect(const GraphicsLayer* graphicsL
 void PaintLayerCompositor::paintContents(const GraphicsLayer* graphicsLayer, GraphicsContext& context, GraphicsLayerPaintingPhase, const IntRect& interestRect) const
 {
     if (graphicsLayer == layerForHorizontalScrollbar())
-        paintScrollbar(m_layoutView.frameView()->horizontalScrollbar(), context, interestRect);
+        paintScrollbar(graphicsLayer, m_layoutView.frameView()->horizontalScrollbar(), context, interestRect);
     else if (graphicsLayer == layerForVerticalScrollbar())
-        paintScrollbar(m_layoutView.frameView()->verticalScrollbar(), context, interestRect);
+        paintScrollbar(graphicsLayer, m_layoutView.frameView()->verticalScrollbar(), context, interestRect);
     else if (graphicsLayer == layerForScrollCorner())
+        // TODO(wkorman): Finish the below.
         FramePainter(*m_layoutView.frameView()).paintScrollCorner(context, interestRect);
 }