Only create PaintChunks at drawing and foreignLayer boundaries

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

Index: third_party/WebKit/Source/platform/graphics/paint/PaintChunker.cpp
diff --git a/third_party/WebKit/Source/platform/graphics/paint/PaintChunker.cpp b/third_party/WebKit/Source/platform/graphics/paint/PaintChunker.cpp
index 2a3e56c0ae77b53a42416110c7ce595efce64f6c..7e34f1e76e3eca1ba87d4ac288a954e2432b5f6c 100644
--- a/third_party/WebKit/Source/platform/graphics/paint/PaintChunker.cpp
+++ b/third_party/WebKit/Source/platform/graphics/paint/PaintChunker.cpp
@@ -8,7 +8,7 @@
 
 namespace blink {
 
-PaintChunker::PaintChunker() {}
+PaintChunker::PaintChunker() : m_skippedItemsSinceLastChunk(0) {}
 
 PaintChunker::~PaintChunker() {}
 
@@ -25,6 +25,10 @@ void PaintChunker::updateCurrentPaintChunkProperties(
 
 bool PaintChunker::incrementDisplayItemIndex(const DisplayItem& item) {
   DCHECK(RuntimeEnabledFeatures::slimmingPaintV2Enabled());
+  if (!PaintChunker::canBeginOrEndChunk(item)) {
+    m_skippedItemsSinceLastChunk++;
+    return false;
+  }
 
 #if DCHECK_IS_ON()
   // Property nodes should never be null because they should either be set to
@@ -50,14 +54,17 @@ bool PaintChunker::incrementDisplayItemIndex(const DisplayItem& item) {
     // from using the same id as the chunk before the foreign layer chunk.
     m_currentChunkId = WTF::nullopt;
   } else {
+    DCHECK(DisplayItem::isDrawingType(item.getType()));
     behavior = DefaultBehavior;
     if (!item.skippedCache() && m_currentChunkId)
       newChunkId.emplace(*m_currentChunkId);
   }
 
   if (m_chunks.isEmpty()) {
-    PaintChunk newChunk(0, 1, newChunkId ? &*newChunkId : nullptr,
-                        m_currentProperties);
+    PaintChunk newChunk(
+        m_skippedItemsSinceLastChunk, m_skippedItemsSinceLastChunk + 1,
+        newChunkId ? &*newChunkId : nullptr, m_currentProperties);
+    m_skippedItemsSinceLastChunk = 0;
     m_chunks.push_back(newChunk);
     m_chunkBehavior.push_back(behavior);
     return true;
@@ -68,12 +75,18 @@ bool PaintChunker::incrementDisplayItemIndex(const DisplayItem& item) {
                           behavior != RequiresSeparateChunk &&
                           m_chunkBehavior.back() != RequiresSeparateChunk;
   if (canContinueChunk) {
+    if (m_skippedItemsSinceLastChunk) {
+      lastChunk.endIndex += m_skippedItemsSinceLastChunk;
+      m_skippedItemsSinceLastChunk = 0;
+    }
     lastChunk.endIndex++;
     return false;
   }
 
-  PaintChunk newChunk(lastChunk.endIndex, lastChunk.endIndex + 1,
+  PaintChunk newChunk(lastChunk.endIndex + m_skippedItemsSinceLastChunk,
+                      lastChunk.endIndex + m_skippedItemsSinceLastChunk + 1,
                       newChunkId ? &*newChunkId : nullptr, m_currentProperties);
+  m_skippedItemsSinceLastChunk = 0;
   m_chunks.push_back(newChunk);
   m_chunkBehavior.push_back(behavior);
   return true;
@@ -83,6 +96,11 @@ bool PaintChunker::decrementDisplayItemIndex() {
   DCHECK(RuntimeEnabledFeatures::slimmingPaintV2Enabled());
   DCHECK(!m_chunks.isEmpty());
 
+  if (m_skippedItemsSinceLastChunk) {
+    m_skippedItemsSinceLastChunk--;
+    return false;
+  }
+
   auto& lastChunk = m_chunks.back();
   if ((lastChunk.endIndex - lastChunk.beginIndex) > 1) {
     lastChunk.endIndex--;
@@ -99,6 +117,7 @@ void PaintChunker::clear() {
   m_chunkBehavior.clear();
   m_currentChunkId = WTF::nullopt;
   m_currentProperties = PaintChunkProperties();
+  m_skippedItemsSinceLastChunk = 0;
 }
 
 Vector<PaintChunk> PaintChunker::releasePaintChunks() {
@@ -107,6 +126,7 @@ Vector<PaintChunk> PaintChunker::releasePaintChunks() {
   m_chunkBehavior.clear();
   m_currentChunkId = WTF::nullopt;
   m_currentProperties = PaintChunkProperties();
+  m_skippedItemsSinceLastChunk = 0;
   return chunks;
 }