MediaRouter: Cache MediaRoutesObserver queries to prevent ext wake-ups

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

Index: chrome/browser/media/router/mojo/media_router_mojo_impl.h
diff --git a/chrome/browser/media/router/mojo/media_router_mojo_impl.h b/chrome/browser/media/router/mojo/media_router_mojo_impl.h
index 73d7187e6f62bfb30c800eb0ea41bf29b462bd12..e088195007c824e312fa95b6b3e85f602cbfb85e 100644
--- a/chrome/browser/media/router/mojo/media_router_mojo_impl.h
+++ b/chrome/browser/media/router/mojo/media_router_mojo_impl.h
@@ -177,6 +177,7 @@ class MediaRouterMojoImpl : public MediaRouterBase,
     // Empty otherwise.
     std::vector<MediaSink> cached_sink_list;
     std::vector<url::Origin> origins;
+
     base::ObserverList<MediaSinksObserver> observers;
 
    private:
@@ -190,6 +191,15 @@ class MediaRouterMojoImpl : public MediaRouterBase,
 
     // 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:
@@ -232,6 +242,11 @@ class MediaRouterMojoImpl : public MediaRouterBase,
   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,