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..6024dd40fe14d76a7661ac5134acd8f5b7eda2a5 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() &&
+      // Here we ignore all document-background paintings because we don't know
+      // if the background is default. ViewPainter will call setFirstPainted()
+      // when a non-default background is painted.
+      displayItem.getType() != DisplayItem::kDocumentBackground &&
+      displayItem.drawsContent()) {
+    m_firstPainted = true;
+  }
+
 #if CHECK_DISPLAY_ITEM_CLIENT_ALIVENESS
   if (!isSkippingCache()) {
     if (displayItem.isCacheable()) {