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 85c449675b38e35c07282ee23625347baf4eb16e..4cee00d8c620d7e69213db9b9eb7281cffaaeff2 100644
--- a/third_party/WebKit/Source/core/dom/IntersectionObserver.h
+++ b/third_party/WebKit/Source/core/dom/IntersectionObserver.h
@@ -33,6 +33,14 @@ class CORE_EXPORT IntersectionObserver final
       Function<void(const HeapVector<Member<IntersectionObserverEntry>>&),
                WTF::SameThreadAffinity>;
 
+  // Defines the assumed initial state of the observed element. If the actual
+  // state is the same as the initial state, then no observation will be
+  // delivered. AUTO means the initial observation will always get sent.
+  enum class InitialState {
+    // TODO(skyostil): Add support for HIDDEN and VISIBLE.
+    AUTO
+  };
+
   static IntersectionObserver* create(const IntersectionObserverInit&,
                                       IntersectionObserverCallback&,
                                       ExceptionState&);
@@ -71,6 +79,9 @@ class CORE_EXPORT IntersectionObserver final
       const {
     return m_observations;
   }
+  // TODO(skyostil): Move this setting to IntersectionObserverInit once the API
+  // is finalized.
+  void setInitialState(InitialState);
 
   DECLARE_TRACE();