Fix first paint tracking for SPv2

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

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "platform/graphics/paint/PaintController.h"
 
 #include "platform/graphics/GraphicsLayer.h"
 #include "platform/graphics/paint/DrawingDisplayItem.h"
 #include "platform/instrumentation/tracing/TraceEvent.h"
 #include "third_party/skia/include/core/SkPictureAnalyzer.h"
@@ skipping 155 matching lines @@
 
 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);
 
+  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()) {
       // Mark the client shouldKeepAlive under this PaintController.
       // The status will end after the new display items are committed.
       displayItem.client().beginShouldKeepAlive(this);
 
       if (!m_currentSubsequenceClients.isEmpty()) {
         // Mark the client shouldKeepAlive under the current subsequence.
         // The status will end when the subsequence owner is invalidated or
@@ skipping 660 matching lines @@
               0, m_newDisplayItemList.size(),
               showPictures ? (DisplayItemList::JsonOptions::ShowPictures |
                               DisplayItemList::JsonOptions::ShowClientDebugName)
                            : DisplayItemList::JsonOptions::ShowClientDebugName)
           ->toPrettyJSONString()
           .utf8()
           .data());
 }
 
 }  // namespace blink