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

Source/platform/graphics/paint/ClipRecorder.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 "platform/graphics/paint/ClipRecorder.h"
 
 #include "platform/RuntimeEnabledFeatures.h"
 #include "platform/graphics/GraphicsContext.h"
 #include "platform/graphics/paint/ClipDisplayItem.h"
 #include "platform/graphics/paint/DisplayItemList.h"
 
 namespace blink {
 
-ClipRecorder::ClipRecorder(GraphicsContext& context, const DisplayItemClientWrapper& client, DisplayItem::Type type, const LayoutRect& clipRect, SkRegion::Op operation)
+ClipRecorder::ClipRecorder(GraphicsContext& context, const DisplayItemClientWrapper& client, DisplayItem::Type type)
     : m_client(client)
     , m_context(context)
     , m_type(type)
+    , m_engaged(false)
 {
-    if (RuntimeEnabledFeatures::slimmingPaintEnabled()) {
-        ASSERT(m_context.displayItemList());
-        if (m_context.displayItemList()->displayItemConstructionIsDisabled())
-            return;
-        m_context.displayItemList()->add(ClipDisplayItem::create(m_client, type, pixelSnappedIntRect(clipRect), operation));
-    } else {
-        ClipDisplayItem clipDisplayItem(m_client, type, pixelSnappedIntRect(clipRect), operation);
-        clipDisplayItem.replay(m_context);
-    }
+}
+
+ClipRecorder::ClipRecorder(GraphicsContext& context, const DisplayItemClientWrapper& client, DisplayItem::Type type, const LayoutRect& clipRect, SkRegion::Op operation)
+    : ClipRecorder(context, client, type)
+{
+    begin(clipRect, operation);
 }
 
 ClipRecorder::~ClipRecorder()
 {
+    if (!m_engaged)
+        return;
+
     DisplayItem::Type endType = DisplayItem::clipTypeToEndClipType(m_type);
     if (RuntimeEnabledFeatures::slimmingPaintEnabled()) {
         ASSERT(m_context.displayItemList());
         if (m_context.displayItemList()->displayItemConstructionIsDisabled())
             return;
         m_context.displayItemList()->add(EndClipDisplayItem::create(m_client, endType));
     } else {
         EndClipDisplayItem endClipDisplayItem(m_client, endType);
         endClipDisplayItem.replay(m_context);
     }
 }
 
+void ClipRecorder::begin(const LayoutRect& clipRect, SkRegion::Op operation)
+{
+    ASSERT(!m_engaged);
+    m_engaged = true;
+
+    if (RuntimeEnabledFeatures::slimmingPaintEnabled()) {
+        ASSERT(m_context.displayItemList());
+        if (m_context.displayItemList()->displayItemConstructionIsDisabled())
+            return;
+        m_context.displayItemList()->add(ClipDisplayItem::create(m_client, m_type, pixelSnappedIntRect(clipRect), operation));
+    } else {
+        ClipDisplayItem clipDisplayItem(m_client, m_type, pixelSnappedIntRect(clipRect), operation);
+        clipDisplayItem.replay(m_context);
+    }
+}
+
 } // namespace blink