Implement interest rects for synchronized paint.

third_party/WebKit/Source/core/frame/FrameView.cpp

 /*
  * Copyright (C) 1998, 1999 Torben Weis <weis@kde.org>
  *                     1999 Lars Knoll <knoll@kde.org>
  *                     1999 Antti Koivisto <koivisto@kde.org>
  *                     2000 Dirk Mueller <mueller@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007, 2008 Apple Inc. All rights reserved.
  *           (C) 2006 Graham Dennis (graham.dennis@gmail.com)
  *           (C) 2006 Alexey Proskuryakov (ap@nypop.com)
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
@@ skipping 2460 matching lines @@
 
     // A null graphics layer can occur for painting of SVG images that are not parented into the main frame tree.
     if (rootGraphicsLayer) {
         synchronizedPaintRecursively(rootGraphicsLayer, interestRect);
     }
     lifecycle().advanceTo(DocumentLifecycle::PaintClean);
 }
 
 void FrameView::synchronizedPaintRecursively(GraphicsLayer* graphicsLayer, const LayoutRect& interestRect)
 {
-    if (graphicsLayer->needsDisplay()) {
-        // TODO(chrishtr): implement interest rects.
-        GraphicsContext context(graphicsLayer->displayItemList());
-        graphicsLayer->paint(context, roundedIntRect(interestRect));
+    GraphicsContext context(graphicsLayer->displayItemList());
 
+    // TODO(chrishtr): fix unit tests to not inject one-off interest rects.
+    if (interestRect != LayoutRect::infiniteRect()) {
+        if (graphicsLayer->needsDisplay()) {
+            graphicsLayer->paint(context, roundedIntRect(interestRect));
+
+            if (!RuntimeEnabledFeatures::slimmingPaintV2Enabled())
+                graphicsLayer->commitIfNeeded();
+        }
+    } else {
+        graphicsLayer->paintIfNeeded(context);
         if (!RuntimeEnabledFeatures::slimmingPaintV2Enabled())
             graphicsLayer->commitIfNeeded();
     }
 
     for (auto& child : graphicsLayer->children()) {
         if (child)
             synchronizedPaintRecursively(child, interestRect);
     }
 }
 
@@ skipping 1435 matching lines @@
 
     if (!graphicsLayer)
         return;
 
     PaintLayer::mapRectToPaintInvalidationBacking(localFrame->contentLayoutObject(), paintInvalidationContainer, viewRect);
 
     graphicsLayerTimingRequests.add(graphicsLayer, Vector<std::pair<int64_t, WebRect>>()).storedValue->value.append(std::make_pair(m_frame->frameID(), enclosingIntRect(viewRect)));
 }
 
 } // namespace blink