[Slimming Paint] Paint the inspector overlay with GraphicsLayer DisplayList.

Source/web/PageOverlay.h

 /*
  * Copyright (C) 2011 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  * 1. Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *
@@ skipping 11 matching lines @@
  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #ifndef PageOverlay_h
 #define PageOverlay_h
 
+#include "platform/graphics/GraphicsLayer.h"
+#include "platform/graphics/GraphicsLayerClient.h"
 #include "wtf/OwnPtr.h"
 #include "wtf/PassOwnPtr.h"
+#include "wtf/text/WTFString.h"
 
 namespace blink {
 
 class GraphicsContext;
 class GraphicsLayer;
 class GraphicsLayerClient;
 class WebPageOverlay;
 class WebViewImpl;
 
-class PageOverlay {
+// Manages a layer than is overlaid on a WebView's content.
+//
+// Clients can paint by providing either exactly one of the following:
+// - WebPageOverlay (which paints using a WebCanvas)
+// - PageOverlay::Painter (which paints using a GraphicsContext)
+//
+// In particular, if a client expects to paint web content (which, when
+// Slimming Paint is enabled, uses a DisplayItemList attached to
+// GraphicsContext), it should provide the latter.
+class PageOverlay : public GraphicsLayerClient {
 public:
+    class Painter {
+    public:
+        // The callee is responsible for saving the GraphicsContext,
+        // if it is required.
+        virtual void paintPageOverlay(GraphicsContext&) = 0;
+    };
+
     static PassOwnPtr<PageOverlay> create(WebViewImpl*, WebPageOverlay*);
+    static PassOwnPtr<PageOverlay> create(WebViewImpl*, Painter*);
 
     ~PageOverlay() { }
 
+    // Exactly one of these should be non-null.
     WebPageOverlay* overlay() const { return m_overlay; }
-    void setOverlay(WebPageOverlay* overlay) { m_overlay = overlay; }
+    Painter* overlayPainter() const { return m_overlayPainter; }
 
     int zOrder() const { return m_zOrder; }
     void setZOrder(int zOrder) { m_zOrder = zOrder; }
 
     void clear();
     void update();
     void paintWebFrame(GraphicsContext&);
 
     GraphicsLayer* graphicsLayer() const { return m_layer.get(); }
 
+    // GraphicsLayerClient implementation
+    void paintContents(const GraphicsLayer*, GraphicsContext&, GraphicsLayerPaintingPhase, const IntRect& inClip) override;
+    String debugName(const GraphicsLayer*) override;
+
 private:
     PageOverlay(WebViewImpl*, WebPageOverlay*);
+    PageOverlay(WebViewImpl*, Painter*);
+
     void invalidateWebFrame();
 
     WebViewImpl* m_viewImpl;
     WebPageOverlay* m_overlay;
-    OwnPtr<GraphicsLayerClient> m_layerClient;
+    Painter* m_overlayPainter;
     OwnPtr<GraphicsLayer> m_layer;
     int m_zOrder;
 };
 
 } // namespace blink
 
 #endif // PageOverlay_h