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..3281fcea96352ef256fc00bd74383250e40b02ac 100644
--- a/third_party/WebKit/Source/core/dom/IntersectionObserver.h
+++ b/third_party/WebKit/Source/core/dom/IntersectionObserver.h
@@ -33,6 +33,15 @@ 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. kAuto means the initial observation will always get sent.
+  enum class InitialState {
+    // TODO(skyostil): Add support for kVisible.
+    kAuto,
+    kHidden,
+  };
+
   static IntersectionObserver* create(const IntersectionObserverInit&,
                                       IntersectionObserverCallback&,
                                       ExceptionState&);
@@ -72,6 +81,12 @@ class CORE_EXPORT IntersectionObserver final
     return m_observations;
   }
 
+  // Set the assumed initial state of the observed element. Note that this can
+  // only be set before calling observe().
+  // TODO(skyostil): Move this setting to IntersectionObserverInit once the API
+  // is finalized.
+  void setInitialState(InitialState);
+
   DECLARE_TRACE();
 
  private:
@@ -90,6 +105,7 @@ class CORE_EXPORT IntersectionObserver final
   Length m_rightMargin;
   Length m_bottomMargin;
   Length m_leftMargin;
+  InitialState m_initialState;
 };
 
 }  // namespace blink