Don't cache subsequence whose layer is not fully contained by repaint rect

Source/platform/graphics/paint/SubsequenceRecorder.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 "platform/graphics/paint/SubsequenceRecorder.h"
 
 #include "platform/RuntimeEnabledFeatures.h"
 #include "platform/graphics/GraphicsContext.h"
 #include "platform/graphics/paint/CachedDisplayItem.h"
@@ skipping 15 matching lines @@
     if (!context.displayItemList()->clientCacheIsValid(client.displayItemClient()))
         return false;
 
     context.displayItemList()->createAndAppend<CachedDisplayItem>(client, DisplayItem::CachedSubsequence);
     return true;
 }
 
 SubsequenceRecorder::SubsequenceRecorder(GraphicsContext& context, const DisplayItemClientWrapper& client)
     : m_displayItemList(context.displayItemList())
     , m_client(client)
+    , m_beginSubsequenceIndex(0)
 {
     if (!RuntimeEnabledFeatures::slimmingPaintV2Enabled())
         return;
 
     ASSERT(m_displayItemList);
+    m_beginSubsequenceIndex = m_displayItemList->newDisplayItems().size();

[chrishtr, 2015/09/08 22:48:00]

You only need access to the size, not the whole vector. Just allowing access to
the former will be safer for the future.

[Xianzhu, 2015/09/09 16:50:33]

It's also needed to set uncacheable flag or a previous begin subsequence display
item (line 63 below).

     m_displayItemList->createAndAppend<BeginSubsequenceDisplayItem>(m_client);
 }
 
 SubsequenceRecorder::~SubsequenceRecorder()
 {
     if (!RuntimeEnabledFeatures::slimmingPaintV2Enabled())
         return;
 
-    // Don't remove no-op BeginSubsequence/EndSubsequence pairs because we need to
-    // match them later with CachedSubsequences.
-    m_displayItemList->createAndAppend<EndSubsequenceDisplayItem>(m_client);
+    if (m_displayItemList->lastDisplayItemIsNoopBegin())
+        m_displayItemList->removeLastDisplayItem();
+    else
+        m_displayItemList->createAndAppend<EndSubsequenceDisplayItem>(m_client);
+}
+
+void SubsequenceRecorder::setUncacheable()
+{
+    if (!RuntimeEnabledFeatures::slimmingPaintV2Enabled())
+        return;
+
+    ASSERT(m_displayItemList->newDisplayItems()[m_beginSubsequenceIndex].type() == DisplayItem::BeginSubsequence);
+    m_displayItemList->newDisplayItems()[m_beginSubsequenceIndex].setUncacheable();
 }
 
 } // namespace blink