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

third_party/WebKit/Source/platform/graphics/paint/PaintController.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 "platform/graphics/paint/PaintController.h"
 
 #include "platform/graphics/GraphicsLayer.h"
 #include "platform/graphics/paint/DrawingDisplayItem.h"
 #include "platform/instrumentation/tracing/TraceEvent.h"
 #include "platform/wtf/AutoReset.h"
@@ skipping 145 matching lines @@
           "under-invalidation: new subsequence wrong length", client, start,
           end);
       CHECK(false);
     }
   }
 
   DCHECK(new_cached_subsequences_.Find(&client) ==
          new_cached_subsequences_.end());
 
   new_cached_subsequences_.insert(&client, SubsequenceMarkers(start, end));
+  last_cached_subsequence_end_ = end;
 }
 
 bool PaintController::LastDisplayItemIsNoopBegin() const {
   if (new_display_item_list_.IsEmpty())
     return false;
 
   const auto& last_display_item = new_display_item_list_.Last();
   return last_display_item.IsBegin() && !last_display_item.DrawsContent();
 }
 
+bool PaintController::LastDisplayItemIsSubsequenceEnd() const {
+  return !new_cached_subsequences_.IsEmpty() &&
+         last_cached_subsequence_end_ == new_display_item_list_.size() - 1;
+}
+
 void PaintController::RemoveLastDisplayItem() {
   if (new_display_item_list_.IsEmpty())
     return;
 
 #if DCHECK_IS_ON()
   // Also remove the index pointing to the removed display item.
   IndicesByClientMap::iterator it = new_display_item_indices_by_client_.Find(
       &new_display_item_list_.Last().Client());
   if (it != new_display_item_indices_by_client_.end()) {
     Vector<size_t>& indices = it->value;
@@ skipping 343 matching lines @@
       !new_display_item_list_.IsEmpty())
     GenerateChunkRasterInvalidationRects(new_paint_chunks_.LastChunk());
 
   SkPictureGpuAnalyzer gpu_analyzer;
 
   current_cache_generation_ =
       DisplayItemClient::CacheGenerationOrInvalidationReason::Next();
 
   new_cached_subsequences_.Swap(current_cached_subsequences_);
   new_cached_subsequences_.Clear();
+  last_cached_subsequence_end_ = 0;
   for (auto& item : current_cached_subsequences_) {
     item.key->SetDisplayItemsCached(current_cache_generation_);
 #if CHECK_DISPLAY_ITEM_CLIENT_ALIVENESS
     DisplayItemClient::EndShouldKeepAliveAllClients(item.key);
 #endif
   }
 
   Vector<const DisplayItemClient*> skipped_cache_clients;
   for (const auto& item : new_display_item_list_) {
     // No reason to continue the analysis once we have a veto.
@@ skipping 375 matching lines @@
               show_paint_records
                   ? (DisplayItemList::JsonOptions::kShowPaintRecords |
                      DisplayItemList::JsonOptions::kShowClientDebugName)
                   : DisplayItemList::JsonOptions::kShowClientDebugName)
           ->ToPrettyJSONString()
           .Utf8()
           .Data());
 }
 
 }  // namespace blink