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

Source/core/paint/ScopeRecorder.cpp

 // Copyright 2015 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/ScopeRecorder.h"
 
 #include "core/layout/LayoutObject.h"
 #include "platform/RuntimeEnabledFeatures.h"
 #include "platform/graphics/GraphicsContext.h"
 #include "platform/graphics/paint/DisplayItemList.h"
 
 namespace blink {
 
-ScopeRecorder::ScopeRecorder(GraphicsContext& context, const LayoutObject& object)
+ScopeRecorder::ScopeRecorder(GraphicsContext& context, const LayoutObject& object, ShouldBegin shouldBegin)
     : m_displayItemList(context.displayItemList())
     , m_object(object)
+    , m_engaged(false)
 {
+    if (shouldBegin == BeginOnConstruction)
+        begin();
+}
+
+ScopeRecorder::~ScopeRecorder()
+{
+    if (!m_engaged)
+        return;
+    if (!RuntimeEnabledFeatures::slimmingPaintEnabled())
+        return;
+
+    m_displayItemList->endScope(m_object.displayItemClient());
+}
+
+void ScopeRecorder::begin()
+{
+    ASSERT(!m_engaged);
+    m_engaged = true;
+
     if (!RuntimeEnabledFeatures::slimmingPaintEnabled())
         return;
 
     ASSERT(m_displayItemList);
     m_displayItemList->beginScope(m_object.displayItemClient());
 }
 
-ScopeRecorder::~ScopeRecorder()
-{
-    if (!RuntimeEnabledFeatures::slimmingPaintEnabled())
-        return;
-
-    m_displayItemList->endScope(m_object.displayItemClient());
-}
-
 } // namespace blink