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

Source/core/paint/CompositingRecorder.cpp

 // 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.
 
 #include "config.h"
 #include "core/paint/CompositingRecorder.h"
 
 #include "core/layout/LayoutObject.h"
 #include "platform/graphics/GraphicsContext.h"
 #include "platform/graphics/GraphicsLayer.h"
 #include "platform/graphics/paint/CompositingDisplayItem.h"
 #include "platform/graphics/paint/DisplayItemList.h"
 
 namespace blink {
 
-CompositingRecorder::CompositingRecorder(GraphicsContext& graphicsContext, const DisplayItemClientWrapper& client, const SkXfermode::Mode xferMode, const float opacity, const FloatRect* bounds, ColorFilter colorFilter)
+CompositingRecorder::CompositingRecorder(GraphicsContext& graphicsContext, const DisplayItemClientWrapper& client)
     : m_client(client)
     , m_graphicsContext(graphicsContext)
+    , m_engaged(false)
 {
-    beginCompositing(graphicsContext, m_client, xferMode, opacity, bounds, colorFilter);
+}
+
+CompositingRecorder::CompositingRecorder(GraphicsContext& graphicsContext, const DisplayItemClientWrapper& client, SkXfermode::Mode xferMode, float opacity, const FloatRect* bounds, ColorFilter colorFilter)
+    : CompositingRecorder(graphicsContext, client)
+{
+    begin(xferMode, opacity, bounds, colorFilter);
 }
 
 CompositingRecorder::~CompositingRecorder()
 {
-    endCompositing(m_graphicsContext, m_client);
+    if (m_engaged)
+        endCompositing(m_graphicsContext, m_client);
+}
+
+void CompositingRecorder::begin(SkXfermode::Mode xferMode, float opacity, const FloatRect* bounds, ColorFilter colorFilter)
+{
+    ASSERT(!m_engaged);
+    m_engaged = true;
+    beginCompositing(m_graphicsContext, m_client, xferMode, opacity, bounds, colorFilter);
 }
 
 void CompositingRecorder::beginCompositing(GraphicsContext& graphicsContext, const DisplayItemClientWrapper& client, const SkXfermode::Mode xferMode, const float opacity, const FloatRect* bounds, ColorFilter colorFilter)
 {
     if (RuntimeEnabledFeatures::slimmingPaintEnabled()) {
         ASSERT(graphicsContext.displayItemList());
         if (graphicsContext.displayItemList()->displayItemConstructionIsDisabled())
             return;
         graphicsContext.displayItemList()->add(BeginCompositingDisplayItem::create(client, xferMode, opacity, bounds, colorFilter));
     } else {
         BeginCompositingDisplayItem beginCompositingDisplayItem(client, xferMode, opacity, bounds, colorFilter);
         beginCompositingDisplayItem.replay(graphicsContext);
     }
 }
 
 void CompositingRecorder::endCompositing(GraphicsContext& graphicsContext, const DisplayItemClientWrapper& client)
 {
     if (RuntimeEnabledFeatures::slimmingPaintEnabled()) {
         ASSERT(graphicsContext.displayItemList());
         if (graphicsContext.displayItemList()->displayItemConstructionIsDisabled())
             return;
         graphicsContext.displayItemList()->add(EndCompositingDisplayItem::create(client));
     } else {
         EndCompositingDisplayItem endCompositingDisplayItem(client);
         endCompositingDisplayItem.replay(graphicsContext);
     }
 }
 
 } // namespace blink