Propogate the tab foreground, background change events to data use

chrome/browser/data_use_measurement/chrome_data_use_ascriber_service.h

Index: chrome/browser/data_use_measurement/chrome_data_use_ascriber_service.h
diff --git a/chrome/browser/data_use_measurement/chrome_data_use_ascriber_service.h b/chrome/browser/data_use_measurement/chrome_data_use_ascriber_service.h
index ce7782ea0e5c3f665ee174f97bdfbf229e2313e1..5e4ef34ccff043b89a145610e52f9ea54dfdf99c 100644
--- a/chrome/browser/data_use_measurement/chrome_data_use_ascriber_service.h
+++ b/chrome/browser/data_use_measurement/chrome_data_use_ascriber_service.h
@@ -6,6 +6,7 @@
 #define CHROME_BROWSER_DATA_USE_MEASUREMENT_CHROME_DATA_USE_ASCRIBER_SERVICE_H_
 
 #include <list>
+#include <unordered_set>
 
 #include "base/macros.h"
 #include "components/keyed_service/core/keyed_service.h"
@@ -53,6 +54,14 @@ class ChromeDataUseAscriberService : public KeyedService {
   // methods cannot be called on the IO thread, so the pointer is cast to void*.
   void ReadyToCommitNavigation(content::NavigationHandle* navigation_handle);
 
+  // Called every time the WebContents changes visibility. Propagates the event
+  // to the |ascriber_| on the IO thread.
+  void WasShownOrHidden(content::RenderFrameHost* main_render_frame_host,
+                        bool visible);
+
+  void RenderFrameHostChanged(content::RenderFrameHost* old_host,

[RyanSturm, 2016/12/13 22:04:20]

nit: Can you add a class comment?

[Raj, 2016/12/14 23:00:50]

Done.

+                              content::RenderFrameHost* new_host);
+
  private:
   friend class ChromeDataUseAscriberServiceTest;
 
@@ -72,6 +81,11 @@ class ChromeDataUseAscriberService : public KeyedService {
   // duration that they are in the queue.
   std::list<content::RenderFrameHost*> pending_frames_queue_;
 
+  // WebContents visibility change events might arrive from the UI thread before
+  // |ascriber_| is set. Sucn pending main render frame visibile events are
+  // maintained in this set and propagated immediately after |ascriber_| is set.
+  std::unordered_set<content::RenderFrameHost*> pending_visible_main_frames_;
+
   DISALLOW_COPY_AND_ASSIGN(ChromeDataUseAscriberService);
 };