Use intersection observer to control frame throttling

third_party/WebKit/Source/core/dom/IntersectionObserver.h

Index: third_party/WebKit/Source/core/dom/IntersectionObserver.h
diff --git a/third_party/WebKit/Source/core/dom/IntersectionObserver.h b/third_party/WebKit/Source/core/dom/IntersectionObserver.h
index cfccf152a5c5754ad6d7b8d4f77656aff5159db4..136cafcc1498abb96b40218de81cd5c0e0dfcb4a 100644
--- a/third_party/WebKit/Source/core/dom/IntersectionObserver.h
+++ b/third_party/WebKit/Source/core/dom/IntersectionObserver.h
@@ -59,6 +59,13 @@ public:
     bool hasEntries() const { return m_entries.size(); }
     const HeapLinkedHashSet<WeakMember<IntersectionObservation>>& observations() const { return m_observations; }
 
+    // A low latency intersection observer delivers events with an immediately
+    // posted task instead of waiting for an idle period (or up to 100ms).
+    // TODO(skyostil): Figure out how we want to expose low latency mode for web
+    // authors and adjust/remove this API accordingly.
+    void setLowLatency(bool lowLatency) { m_lowLatency = lowLatency; }
+    bool lowLatency() const { return m_lowLatency; }
+
     DECLARE_TRACE();
 
 private:
@@ -74,6 +81,7 @@ private:
     Length m_rightMargin;
     Length m_bottomMargin;
     Length m_leftMargin;
+    bool m_lowLatency;
 };
 
 } // namespace blink