Implement interfaces in PaintInfo and make it a class.

Source/core/platform/graphics/GraphicsContextAnnotation.h

Index: Source/core/platform/graphics/GraphicsContextAnnotation.h
diff --git a/Source/core/platform/graphics/GraphicsContextAnnotation.h b/Source/core/platform/graphics/GraphicsContextAnnotation.h
index 22684b5a1adc41178891542b166f107dcc017e97..c2c3e559b6455623ba6884c862a8ce7b2e7dd113 100644
--- a/Source/core/platform/graphics/GraphicsContextAnnotation.h
+++ b/Source/core/platform/graphics/GraphicsContextAnnotation.h
@@ -36,14 +36,14 @@
 
 #define ANNOTATE_GRAPHICS_CONTEXT(paintInfo, renderer) \
     GraphicsContextAnnotator scopedGraphicsContextAnnotator; \
-    if (UNLIKELY(paintInfo.context->annotationMode())) \
+    if (UNLIKELY(paintInfo.getContext()->annotationMode()))             \
         scopedGraphicsContextAnnotator.annotate(paintInfo, renderer)
 
 namespace WebCore {
 
 class GraphicsContext;
+class PaintInfo;
 class RenderObject;
-struct PaintInfo;
 
 enum AnnotationMode {
     AnnotateRendererName    = 1 << 0,
@@ -60,7 +60,7 @@ typedef Vector<std::pair<const char*, String> > AnnotationList;
 
 class GraphicsContextAnnotation {
 public:
-    GraphicsContextAnnotation(const PaintInfo&, const RenderObject*);
+    GraphicsContextAnnotation(PaintInfo&, const RenderObject*);

[do-not-use, 2013/08/05 11:16:30]

I guess we could have 2 context getters so that we can keep the const here:
GraphicsContext* context() { return m_context; }
const GraphicsContext* context() const { return m_context; }

 
     String rendererName() const { return ASCIILiteral(m_rendererName); }
     String paintPhase() const { return ASCIILiteral(m_paintPhase); }
@@ -90,7 +90,7 @@ public:
             finishAnnotation();
     }
 
-    void annotate(const PaintInfo&, const RenderObject*);
+    void annotate(PaintInfo&, const RenderObject*);
 
 private:
     void finishAnnotation();