Don't allow the composited-alpha folding optimization to cross subsequences

third_party/WebKit/Source/platform/graphics/paint/PaintController.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 PaintController_h
 #define PaintController_h
 
 #include <memory>
 #include <utility>
 #include "platform/PlatformExport.h"
@@ skipping 191 matching lines @@
   void BeginShouldKeepAlive(const DisplayItemClient&);
 
   void BeginSubsequence(const DisplayItemClient& client) {
     current_subsequence_clients_.push_back(&client);
     BeginShouldKeepAlive(client);
   }
 
   void EndSubsequence() { current_subsequence_clients_.pop_back(); }
 #endif
 
+  bool LastDisplayItemIsSubsequenceEnd() const;
+
  protected:
   PaintController()
       : new_display_item_list_(0),
         construction_disabled_(false),
         subsequence_caching_disabled_(false),
         first_painted_(false),
         text_painted_(false),
         image_painted_(false),
         skipping_cache_count_(0),
         num_cached_new_items_(0),
         current_cached_subsequence_begin_index_in_new_list_(kNotFound),
 #ifndef NDEBUG
         num_sequential_matches_(0),
         num_out_of_order_matches_(0),
         num_indexed_items_(0),
 #endif
         under_invalidation_checking_begin_(0),
-        under_invalidation_checking_end_(0) {
+        under_invalidation_checking_end_(0),
+        last_cached_subsequence_end_(0) {
     ResetCurrentListIndices();
     SetTracksRasterInvalidations(
         RuntimeEnabledFeatures::paintUnderInvalidationCheckingEnabled());
   }
 
  private:
   friend class PaintControllerTestBase;
   friend class PaintControllerPaintTestBase;
 
   bool LastDisplayItemIsNoopBegin() const;
@@ skipping 172 matching lines @@
 
 #if CHECK_DISPLAY_ITEM_CLIENT_ALIVENESS
   // A stack recording subsequence clients that are currently painting.
   Vector<const DisplayItemClient*> current_subsequence_clients_;
 #endif
 
   typedef HashMap<const DisplayItemClient*, SubsequenceMarkers>
       CachedSubsequenceMap;
   CachedSubsequenceMap current_cached_subsequences_;
   CachedSubsequenceMap new_cached_subsequences_;
+  size_t last_cached_subsequence_end_;
 
   FRIEND_TEST_ALL_PREFIXES(PaintControllerTest, CachedSubsequenceSwapOrder);
   FRIEND_TEST_ALL_PREFIXES(PaintControllerTest, CachedNestedSubsequenceUpdate);
 };
 
 }  // namespace blink
 
 #endif  // PaintController_h