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..4dc47881884b36d836f9427f4525bcc2adc3b0ee 100644
--- a/third_party/WebKit/Source/platform/graphics/paint/PaintController.cpp
+++ b/third_party/WebKit/Source/platform/graphics/paint/PaintController.cpp
@@ -525,6 +525,15 @@ void PaintController::commitNewDisplayItems(
       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)