Fix crash in SiteEngagementServiceHelper when switching render view hosts.

chrome/browser/engagement/site_engagement_helper.h

Index: chrome/browser/engagement/site_engagement_helper.h
diff --git a/chrome/browser/engagement/site_engagement_helper.h b/chrome/browser/engagement/site_engagement_helper.h
index 68d4f32b390e9bb736150f1b9ccf8f6fcf5ee80f..c7f9e65206c2c8dd1790fa0e15dda265a945baed 100644
--- a/chrome/browser/engagement/site_engagement_helper.h
+++ b/chrome/browser/engagement/site_engagement_helper.h
@@ -78,12 +78,14 @@ class SiteEngagementHelper
     void Stop();
 
     // Returns whether the InputTracker has been started for a RenderViewHost.
-    bool is_active() const { return is_active_; }
+    bool IsActive() const;
 
     // Returns whether input tracking callbacks have been added to
     // RenderViewHost.
     bool is_tracking() const { return is_tracking_; }
 
+    content::RenderViewHost* host() const { return host_; }
+
     // Set the timer object for testing purposes.
     void SetPauseTimerForTesting(scoped_ptr<base::Timer> timer);
 
@@ -100,7 +102,6 @@ class SiteEngagementHelper
     content::RenderViewHost* host_;
     content::RenderWidgetHost::KeyPressEventCallback key_press_event_callback_;
     content::RenderWidgetHost::MouseEventCallback mouse_event_callback_;
-    bool is_active_;
     bool is_tracking_;
   };