Intersection Observer first draft

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

Index: third_party/WebKit/Source/core/frame/FrameView.cpp
diff --git a/third_party/WebKit/Source/core/frame/FrameView.cpp b/third_party/WebKit/Source/core/frame/FrameView.cpp
index d27feb25d9efcfc466580789bf8518fade265c11..c1e3d78b6464b94998f9c19fa9735bae22faf166 100644
--- a/third_party/WebKit/Source/core/frame/FrameView.cpp
+++ b/third_party/WebKit/Source/core/frame/FrameView.cpp
@@ -1089,6 +1089,27 @@ void FrameView::invalidateTreeIfNeeded(PaintInvalidationState& paintInvalidation
 
     m_doFullPaintInvalidation = false;
     lifecycle().advanceTo(DocumentLifecycle::PaintInvalidationClean);
+
+    if (RuntimeEnabledFeatures::intersectionObserverEnabled()) {
+        computeIntersectionObservations(paintInvalidationState);
+    }
+}
+
+void FrameView::computeIntersectionObservations(PaintInvalidationState& paintInvalidationState)
+{
+    ASSERT(layoutView());
+
+    if (FrameView* parent = parentFrameView()) {
+        m_clippedBounds = IntRect(frameRect().location(), paintInvalidationState.clipRect().pixelSnappedSize());
+        m_clippedBounds = parent->contentsToRootFrame(m_clippedBounds);
+        m_clippedBounds.intersect(parent->contentsToRootFrame(parent->m_clippedBounds));
+        if (!m_clippedBounds.isEmpty())
+            m_clippedBounds = rootFrameToContents(m_clippedBounds);
+    } else {
+        m_clippedBounds = pixelSnappedIntRect(paintInvalidationState.clipRect());
+    }
+
+    layoutView()->computeIntersectionObservations(FloatRect(m_clippedBounds));
 }
 
 DocumentLifecycle& FrameView::lifecycle() const