Include viewport visibility checks for autoplay experiment.

Source/core/html/AutoplayExperimentHelper.h

Index: Source/core/html/AutoplayExperimentHelper.h
diff --git a/Source/core/html/AutoplayExperimentHelper.h b/Source/core/html/AutoplayExperimentHelper.h
index c9d015f062bce1126923f2ec3613ad7067c92219..f3388280a9407f273554ada91d54e01cc891a9a2 100644
--- a/Source/core/html/AutoplayExperimentHelper.h
+++ b/Source/core/html/AutoplayExperimentHelper.h
@@ -79,12 +79,51 @@ public:
     void mutedChanged();
     void positionChanged();
 
+    // For testing.
+    void triggerAutoplayViewportCheck();
+
 private:
+    // The location and size of our element, and the viewport.  Also supports
+    // "not valid", in case some of the information isn't available.
+    class LocationState {
+    public:
+        LocationState() : m_valid(false) {}
+        LocationState(Element&);
+
+        bool valid() const { return m_valid; }
+        PageVisibilityState visibilityState() const { return m_visibilityState; }
+        const IntRect& element() const { return m_element; }
+        const IntRect& screen() const { return m_screen; }
+
+        bool operator==(const LocationState&) const;
+        bool operator!=(const LocationState&) const;
+
+        // Return true if and only if the player is visible.
+        bool isInViewport();
+
+    private:
+        bool m_valid;
+        PageVisibilityState m_visibilityState;
+        IntRect m_element;
+        IntRect m_screen;
+    };
+
+    // Register to receive position updates, if we haven't already.  If we
+    // have, then this does nothing.
+    void registerForPositionUpdatesIfNeeded();
+
+    // Un-register for position updates, if we are currently registered.
+    void unregisterForPositionUpdatesIfNeeded();
+
     // Return true if any only if this player meets (most) of the eligibility
     // requirements for the experiment to override the need for a user
     // gesture.  This includes everything except the visibility test.
     bool isEligible() const;
 
+    // Return false if and only if the player is not visible, and we care
+    // that it must be visible.
+    bool isInViewportIfNeeded();
+
     // Set the muted flag on the media if we're in an experiment mode that
     // requires it, else do nothing.
     void muteIfNeeded();
@@ -98,6 +137,9 @@ private:
     // there are several different cases.
     void prepareToPlay(AutoplayMetrics);
 
+    // Process a timer for checking visibility.
+    void viewportTimerFired(Timer<AutoplayExperimentHelper>*);
+
     // Return our media element's document.
     Document& document() const;
 
@@ -115,6 +157,14 @@ private:
     // True if we've received a play() without a pause().
     bool m_playPending : 1;
 
+    // Are we registered with the view for position updates?
+    bool m_registeredWithView : 1;
+
+    // According to our last position update, are we in the viewport?
+    bool m_wasInViewport : 1;
+
+    Timer<AutoplayExperimentHelper> m_viewportTimer;
+
     friend class Internals;
 };