[Slimming Paint] Paint the inspector overlay with GraphicsLayer DisplayList.

Source/web/PageOverlayList.cpp

Index: Source/web/PageOverlayList.cpp
diff --git a/Source/web/PageOverlayList.cpp b/Source/web/PageOverlayList.cpp
index f5b99ffa5642c655d8af3d766c639b8df0224852..e690ffceba2c48bb482a43452637912976b2cd64 100644
--- a/Source/web/PageOverlayList.cpp
+++ b/Source/web/PageOverlayList.cpp
@@ -114,6 +114,9 @@ void PageOverlayList::update()
 
 void PageOverlayList::paintWebFrame(GraphicsContext& gc)
 {
+    // If accelerated compositing is active, page overlays are painted through
+    // their corresponding GraphicsLayer.
+    ASSERT(!m_viewImpl->isAcceleratedCompositingActive());
     for (size_t i = 0; i < m_pageOverlays.size(); ++i)
         m_pageOverlays[i]->paintWebFrame(gc);
 }
@@ -136,4 +139,11 @@ size_t PageOverlayList::findGraphicsLayer(GraphicsLayer* layer)
     return WTF::kNotFound;
 }
 
+GraphicsLayer* PageOverlayList::graphicsLayerForTesting() const
+{
+    if (m_pageOverlays.isEmpty())
+        return nullptr;
+    return m_pageOverlays[0]->graphicsLayer();
+}
+
 } // namespace blink