Fold compositing display items into contained drawings if the drawing is a singleton.

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 ecdfc3a5988db41f4d3f342ca2101f7733e2581f..dcb96b39b3063eb514e91bad473613871c33c727 100644
--- a/third_party/WebKit/Source/platform/graphics/paint/PaintController.cpp
+++ b/third_party/WebKit/Source/platform/graphics/paint/PaintController.cpp
@@ -153,6 +153,13 @@ void PaintController::removeLastDisplayItem()
         m_newPaintChunks.decrementDisplayItemIndex();
 }
 
+const DisplayItem* PaintController::lastDisplayItem(unsigned offset)
+{
+    if (offset < m_newDisplayItemList.size())
+        return &m_newDisplayItemList[m_newDisplayItemList.size() - offset - 1];
+    return nullptr;
+}
+
 void PaintController::processNewItem(DisplayItem& displayItem)
 {
     DCHECK(!m_constructionDisabled);
@@ -422,6 +429,8 @@ void PaintController::commitNewDisplayItems(const LayoutSize& offsetFromLayoutOb
 
         if (item.isCacheable())
             item.client().setDisplayItemsCached(m_currentCacheGeneration);
+        else
+            item.client().setDisplayItemsUncached();

[chrishtr, 2016/07/27 17:47:48]

@xianzhu: added this. WDYT?

[Xianzhu, 2016/07/27 18:00:19]

This has a problem that if any cacheable display item is after skipped-cache
display item for the client, the uncached status will be overriden.

You also need to check item.skippedCache() because non-drawing and
non-subsequence display items are also not cacheable.

     }
 
     // The new list will not be appended to again so we can release unused memory.