Only create PaintChunks at drawing and foreignLayer boundaries

third_party/WebKit/Source/platform/graphics/paint/PaintController.cpp

Index: third_party/WebKit/Source/platform/graphics/paint/PaintController.cpp
diff --git a/third_party/WebKit/Source/platform/graphics/paint/PaintController.cpp b/third_party/WebKit/Source/platform/graphics/paint/PaintController.cpp
index 0df90d0a9753d32a449ab89e0a001078987f05ec..f2a20150d66f9d0977fe4ee46d85d7d716d4b295 100644
--- a/third_party/WebKit/Source/platform/graphics/paint/PaintController.cpp
+++ b/third_party/WebKit/Source/platform/graphics/paint/PaintController.cpp
@@ -415,16 +415,23 @@ void PaintController::copyCachedSubsequence(size_t& cachedItemIndex) {
 
   DisplayItem::Id endSubsequenceId(cachedItem->client(),
                                    DisplayItem::kEndSubsequence);
-  Vector<PaintChunk>::const_iterator cachedChunk;
+  Vector<PaintChunk>::const_iterator nextCachedChunk =
+      m_currentPaintArtifact.paintChunks().end();
   if (RuntimeEnabledFeatures::slimmingPaintV2Enabled()) {
-    cachedChunk =
-        m_currentPaintArtifact.findChunkByDisplayItemIndex(cachedItemIndex);
-    DCHECK(cachedChunk != m_currentPaintArtifact.paintChunks().end());
-    updateCurrentPaintChunkProperties(
-        cachedChunk->id ? &*cachedChunk->id : nullptr, cachedChunk->properties);
-  } else {
-    // Avoid uninitialized variable error on Windows.
-    cachedChunk = m_currentPaintArtifact.paintChunks().begin();
+    // Skip over any items that can't be paint chunk boundaries to find the
+    // first chunk following |cachedItemIndex|.
+    size_t nextChunkIndex = cachedItemIndex + 1;
+    for (; nextChunkIndex < m_currentPaintArtifact.getDisplayItemList().size();
+         nextChunkIndex++) {
+      const auto& item =
+          m_currentPaintArtifact.getDisplayItemList()[nextChunkIndex];
+      if (PaintChunker::canBeginOrEndChunk(item)) {
+        nextCachedChunk =
+            m_currentPaintArtifact.findChunkByDisplayItemIndex(nextChunkIndex);
+        DCHECK(nextCachedChunk != m_currentPaintArtifact.paintChunks().end());
+        break;
+      }
+    }
   }
 
   while (true) {
@@ -436,17 +443,14 @@ void PaintController::copyCachedSubsequence(size_t& cachedItemIndex) {
     bool metEndSubsequence = cachedItem->getId() == endSubsequenceId;
     if (!RuntimeEnabledFeatures::paintUnderInvalidationCheckingEnabled()) {
       if (RuntimeEnabledFeatures::slimmingPaintV2Enabled() &&
-          cachedItemIndex == cachedChunk->endIndex) {
-        ++cachedChunk;
-        DCHECK(cachedChunk != m_currentPaintArtifact.paintChunks().end());
+          nextCachedChunk != m_currentPaintArtifact.paintChunks().end() &&
+          cachedItemIndex == nextCachedChunk->beginIndex) {
         updateCurrentPaintChunkProperties(
-            cachedChunk->id ? &*cachedChunk->id : nullptr,
-            cachedChunk->properties);
+            nextCachedChunk->id ? &*nextCachedChunk->id : nullptr,
+            nextCachedChunk->properties);
+        nextCachedChunk++;
       }
       processNewItem(moveItemFromCurrentListToNewList(cachedItemIndex));
-      if (RuntimeEnabledFeatures::slimmingPaintV2Enabled())
-        DCHECK((!m_newPaintChunks.lastChunk().id && !cachedChunk->id) ||
-               m_newPaintChunks.lastChunk().matches(*cachedChunk));
     }
 
     ++cachedItemIndex;