Fix first paint tracking for SPv2

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 4f0fc551f1ad0ec13d3c1c1fc29fbc8e28792ba3..d993b19d9843eaeb4492b169eecb1e02a2514be0 100644
--- a/third_party/WebKit/Source/platform/graphics/paint/PaintController.cpp
+++ b/third_party/WebKit/Source/platform/graphics/paint/PaintController.cpp
@@ -173,6 +173,15 @@ const DisplayItem* PaintController::lastDisplayItem(unsigned offset) {
 void PaintController::processNewItem(DisplayItem& displayItem) {
   DCHECK(!m_constructionDisabled);
 
+  if (!m_firstPainted && displayItem.isDrawing() &&

[pdr., 2017/01/12 21:56:45]

processNewItem is pretty hot so I'm worried about adding a branch here. Could we
put this check in commitNewDisplayItems instead, which is called less
frequently? Doing this would require iterating through the first few items to
find a painted one.

[Xianzhu, 2017/01/12 22:13:39]

Good idea. Done.

+      // Here we ignore all document-background paintings because we don't know
+      // if the background is default. ViewPainter should have called
+      // setFirstPainted() if this display item is for non-default background.
+      displayItem.getType() != DisplayItem::kDocumentBackground &&
+      displayItem.drawsContent()) {
+    m_firstPainted = true;
+  }
+
 #if CHECK_DISPLAY_ITEM_CLIENT_ALIVENESS
   if (!isSkippingCache()) {
     if (displayItem.isCacheable()) {