MediaRouter: Cache MediaRoutesObserver queries to prevent ext wake-ups

chrome/browser/media/router/mojo/media_router_mojo_impl.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CHROME_BROWSER_MEDIA_ROUTER_MOJO_MEDIA_ROUTER_MOJO_IMPL_H_
 #define CHROME_BROWSER_MEDIA_ROUTER_MOJO_MEDIA_ROUTER_MOJO_IMPL_H_
 
 #include <stdint.h>
 
 #include <deque>
@@ skipping 159 matching lines @@
     // True if the query has been sent to the MRPM.
     bool is_active = false;
 
     // True if cached result is available.
     bool has_cached_result = false;
 
     // Cached list of sinks for the query, if |has_cached_result| is true.
     // Empty otherwise.
     std::vector<MediaSink> cached_sink_list;
     std::vector<url::Origin> origins;
+
     base::ObserverList<MediaSinksObserver> observers;
 
    private:
     DISALLOW_COPY_AND_ASSIGN(MediaSinksQuery);
   };
 
   struct MediaRoutesQuery {
    public:
     MediaRoutesQuery();
     ~MediaRoutesQuery();
 
     // True if the query has been sent to the MRPM.  False otherwise.
     bool is_active = false;
+
+    // True if cached result is available.
+    bool has_cached_result = false;

[Wez, 2017/03/04 02:07:32]

nit: Since you have two cached-data fields below this seems fine, but would it
be possible to restructure things to use base::Optional<>..?

[miu, 2017/03/04 02:24:39]

Done.

+
+    // Cached list of routes for the query, if |has_cached_result| is true.
+    // Empty otherwise.
+    std::vector<MediaRoute> cached_route_list;
+    std::vector<std::string> joinable_route_ids;
+
     base::ObserverList<MediaRoutesObserver> observers;
 
    private:
     DISALLOW_COPY_AND_ASSIGN(MediaRoutesQuery);
   };
 
   // Standard constructor, used by
   // MediaRouterMojoImplFactory::GetApiForBrowserContext.
   explicit MediaRouterMojoImpl(
       extensions::EventPageTracker* event_page_tracker);
@@ skipping 22 matching lines @@
   // MediaRouter implementation.
   bool RegisterMediaSinksObserver(MediaSinksObserver* observer) override;
   void UnregisterMediaSinksObserver(MediaSinksObserver* observer) override;
   void RegisterMediaRoutesObserver(MediaRoutesObserver* observer) override;
   void UnregisterMediaRoutesObserver(MediaRoutesObserver* observer) override;
   void RegisterIssuesObserver(IssuesObserver* observer) override;
   void UnregisterIssuesObserver(IssuesObserver* observer) override;
   void RegisterRouteMessageObserver(RouteMessageObserver* observer) override;
   void UnregisterRouteMessageObserver(RouteMessageObserver* observer) override;
 
+  // Notifies |observer| of any existing cached routes, after registration.
+  void NotifyOfExistingRoutesAfterRegistration(

[Wez, 2017/03/04 02:07:32]

This is a confusing name, IMO - I'd suggest either calling it
NotifyOfExistingRoutes and having the comment explain that the observer must be
registered, or calling it NotifyOfExistingRoutesIfRegistered, since it's
actually conditional on the observer _still_ being registered.

Or, call it FinishRegisterMediaRoutesOberver, since that's in effect what it's
doing; though that would raise the question of why this is the only form of
observer that needs a separate step for that

[miu, 2017/03/04 02:24:39]

Done.

+      const MediaSource::Id& source_id,
+      MediaRoutesObserver* observer) const;
+
   // These calls invoke methods in the component extension via Mojo.
   void DoCreateRoute(const MediaSource::Id& source_id,
                      const MediaSink::Id& sink_id,
                      const url::Origin& origin,
                      int tab_id,
                      const std::vector<MediaRouteResponseCallback>& callbacks,
                      base::TimeDelta timeout,
                      bool incognito);
   void DoJoinRoute(const MediaSource::Id& source_id,
                    const std::string& presentation_id,
@@ skipping 185 matching lines @@
 #endif
 
   base::WeakPtrFactory<MediaRouterMojoImpl> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(MediaRouterMojoImpl);
 };
 
 }  // namespace media_router
 
 #endif  // CHROME_BROWSER_MEDIA_ROUTER_MOJO_MEDIA_ROUTER_MOJO_IMPL_H_