Allow certain SP recorder classes to defer their "begin" operation.

Source/core/paint/CompositingRecorder.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CompositingRecorder_h
 #define CompositingRecorder_h
 
 #include "platform/geometry/FloatRect.h"
 #include "platform/graphics/GraphicsTypes.h"
 #include "platform/graphics/paint/DisplayItem.h"
 #include "public/platform/WebBlendMode.h"
 
 namespace blink {
 
 class GraphicsContext;
 class LayoutObject;
 
 class CompositingRecorder {
 public:
-    CompositingRecorder(GraphicsContext&, const DisplayItemClientWrapper&, const SkXfermode::Mode, const float opacity, const FloatRect* bounds = 0, ColorFilter = ColorFilterNone);
+    CompositingRecorder(GraphicsContext&, const DisplayItemClientWrapper&);
+    CompositingRecorder(GraphicsContext&, const DisplayItemClientWrapper&, SkXfermode::Mode, float opacity, const FloatRect* bounds = 0, ColorFilter = ColorFilterNone);
+    ~CompositingRecorder();
 
-    ~CompositingRecorder();
+    void begin(SkXfermode::Mode, float opacity, const FloatRect* bounds = 0, ColorFilter = ColorFilterNone);
 
     // FIXME: These helpers only exist to ease the transition to slimming paint
     //        and should be removed once slimming paint is enabled by default.
     static void beginCompositing(GraphicsContext&, const DisplayItemClientWrapper&, const SkXfermode::Mode, const float opacity, const FloatRect* bounds = 0, ColorFilter = ColorFilterNone);
     static void endCompositing(GraphicsContext&, const DisplayItemClientWrapper&);
 
 private:
     DisplayItemClientWrapper m_client;
     GraphicsContext& m_graphicsContext;
+    bool m_engaged;
 };
 
 } // namespace blink
 
 #endif // CompositingRecorder_h