Intersection Observer first draft

Source/core/frame/FrameView.h

Index: Source/core/frame/FrameView.h
diff --git a/Source/core/frame/FrameView.h b/Source/core/frame/FrameView.h
index 2b927493980b7533a852fb49cf5caf9c8f46bd55..0cd0dd6a6b259bd670bf2795c3a210edf1d567ba 100644
--- a/Source/core/frame/FrameView.h
+++ b/Source/core/frame/FrameView.h
@@ -716,6 +716,8 @@ private:
     void collectFrameTimingRequests(GraphicsLayerFrameTimingRequests&);
     void collectFrameTimingRequestsRecursive(GraphicsLayerFrameTimingRequests&);
 
+    void computeIntersectionObservations(PaintInvalidationState&);
+
     LayoutSize m_size;
 
     typedef HashSet<RefPtr<LayoutEmbeddedObject>> EmbeddedObjectSet;
@@ -838,6 +840,10 @@ private:
     // TODO(bokan): crbug.com/484188. We should specialize FrameView for the
     // main frame.
     OwnPtrWillBeMember<ScrollableArea> m_viewportScrollableArea;
+
+    // This frame's bounds in the root frame's content coordinates, clipped
+    // recursively through every ancestor view.
+    IntRect m_clippedBounds;
 };
 
 inline void FrameView::incrementVisuallyNonEmptyCharacterCount(unsigned count)