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 507 matching lines @@
         visualRectForDisplayItem(item, offsetFromLayoutObject));
 
     if (item.isCacheable()) {
       item.client().setDisplayItemsCached(m_currentCacheGeneration);
     } else {
       if (item.client().isJustCreated())
         item.client().clearIsJustCreated();
       if (item.skippedCache())
         skippedCacheClients.push_back(&item.client());
     }
+
+    if (UNLIKELY(!m_firstPainted) && item.isDrawing() &&

[pdr., 2017/01/12 22:21:55]

This will still be called for all new and cached items. WDYT about pulling this
out of the loop? Something like this on line 505:
if (!m_firstPainted) {
  for (const auto& item : m_newDisplayItemList) {
    if (item.isDrawing() && ...) {
      m_firstPainted = true;
      break;
    }
  }
}

[Xianzhu, 2017/01/12 22:32:22]

Done.

Considered this but thought the cost of 'if (UNLIKELY(!m_firstPainted)...)' in
the loop was comparable to that of an iteration of a separate loop. Overlooked
the fact that we won't execute the loop at all if m_firstPaint is true.

+        // 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.
+        item.getType() != DisplayItem::kDocumentBackground &&
+        item.drawsContent()) {
+      m_firstPainted = true;
+    }
   }
 
   for (auto* client : skippedCacheClients)
     client->setDisplayItemsUncached();
 
   // The new list will not be appended to again so we can release unused memory.
   m_newDisplayItemList.shrinkToFit();
   m_currentPaintArtifact = PaintArtifact(
       std::move(m_newDisplayItemList), m_newPaintChunks.releasePaintChunks(),
       gpuAnalyzer.suitableForGpuRasterization());
@@ skipping 308 matching lines @@
               0, m_newDisplayItemList.size(),
               showPictures ? (DisplayItemList::JsonOptions::ShowPictures |
                               DisplayItemList::JsonOptions::ShowClientDebugName)
                            : DisplayItemList::JsonOptions::ShowClientDebugName)
           ->toPrettyJSONString()
           .utf8()
           .data());
 }
 
 }  // namespace blink