Only create PaintChunks at drawing and foreignLayer boundaries

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

Index: third_party/WebKit/Source/platform/graphics/paint/PaintChunker.h
diff --git a/third_party/WebKit/Source/platform/graphics/paint/PaintChunker.h b/third_party/WebKit/Source/platform/graphics/paint/PaintChunker.h
index ff6da1fc0b7ddf852ab94f4f00df3a654499ea83..23d3fb9d7a80e6a5997c89293556b94e1272b73a 100644
--- a/third_party/WebKit/Source/platform/graphics/paint/PaintChunker.h
+++ b/third_party/WebKit/Source/platform/graphics/paint/PaintChunker.h
@@ -15,9 +15,13 @@
 
 namespace blink {
 
-// Accepts information about changes to |PaintChunkProperties| as drawings are
-// accumulated, and produces a series of paint chunks: contiguous ranges of the
-// display list with identical |PaintChunkProperties|.
+// Accepts information about changes to |PaintChunkProperties| as drawings and
+// foreign layers [1] are accumulated, and produces a series of paint chunks:
+// contiguous ranges of the display list with identical |PaintChunkProperties|.
+//
+// [1] Only drawings and foreign layers are used for compositing (i.e., other
+// display item types are ignored by PaintArtifactCompositor), so other types
+// do not create paint chunks as an optimization (see: canBeginOrEndChunk).
 class PLATFORM_EXPORT PaintChunker final {
   DISALLOW_NEW();
   WTF_MAKE_NONCOPYABLE(PaintChunker);
@@ -27,7 +31,9 @@ class PLATFORM_EXPORT PaintChunker final {
   ~PaintChunker();
 
   bool isInInitialState() const {
-    return m_chunks.isEmpty() && m_currentProperties == PaintChunkProperties();
+    return m_chunks.isEmpty() &&
+           m_currentProperties == PaintChunkProperties() &&
+           m_skippedItemsSinceLastChunk == 0;
   }
 
   const PaintChunkProperties& currentPaintChunkProperties() const {
@@ -41,6 +47,13 @@ class PLATFORM_EXPORT PaintChunker final {
   // Returns true if the last chunk is removed.
   bool decrementDisplayItemIndex();
 
+  // Paint chunks are only created/ended at drawing and foreign layer boundaries
+  // with all other types being skipped (see: m_skippedItemsSinceLastChunk).
+  static bool canBeginOrEndChunk(const DisplayItem& item) {
+    return DisplayItem::isDrawingType(item.getType()) ||
+           DisplayItem::isForeignLayerType(item.getType());
+  }
+
   PaintChunk& paintChunkAt(size_t i) { return m_chunks[i]; }
   size_t lastChunkIndex() const {
     return m_chunks.isEmpty() ? kNotFound : m_chunks.size() - 1;
@@ -72,6 +85,7 @@ class PLATFORM_EXPORT PaintChunker final {
   Vector<ItemBehavior> m_chunkBehavior;
   Optional<PaintChunk::Id> m_currentChunkId;
   PaintChunkProperties m_currentProperties;
+  size_t m_skippedItemsSinceLastChunk;
 };
 
 }  // namespace blink