Dispatch geolocation IPCs on the UI thread. Aside from simplifying the code to avoid a lot of threa…

content/public/browser/geolocation_provider.h

 // Copyright (c) 2012 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 CONTENT_PUBLIC_BROWSER_GEOLOCATION_PROVIDER_H_
 #define CONTENT_PUBLIC_BROWSER_GEOLOCATION_PROVIDER_H_
 
-#include "base/callback_forward.h"
+#include "base/callback_list.h"
 #include "content/common/content_export.h"
 
 namespace content {
 struct Geoposition;
 
-class CONTENT_EXPORT GeolocationProvider {
+// This is the main API to the geolocation subsystem. The application will hold
+// a single instance of this class and can register multiple clients to be
+// notified of location changes:
+// * Callbacks are registered by AddLocationUpdateCallback() and will keep
+//   receiving updates until the returned subscription object is destructed.
+// The application must instantiate the GeolocationProvider on the UI thread and
+// must communicate with it on the same thread.
+// The underlying location arbitrator will only be enabled whilst there is at
+// least one registered observer or pending callback (and only after
+// UserDidOptIntoLocationServices). The arbitrator and the location providers it
+// uses run on a separate Geolocation thread.
+class GeolocationProvider {
  public:
-  // This method, and all below, can only be called on the IO thread unless
-  // otherwise specified.
-  static GeolocationProvider* GetInstance();
+  CONTENT_EXPORT static GeolocationProvider* GetInstance();
 
   typedef base::Callback<void(const Geoposition&)> LocationUpdateCallback;
+  typedef base::CallbackList<void(const Geoposition&)>::Subscription
+      Subscription;
 
   // |use_high_accuracy| is used as a 'hint' for the provider preferences for
   // this particular observer, however the observer could receive updates for
   // best available locations from any active provider whilst it is registered.
-  // If an existing observer is added a second time, its options are updated
-  // but only a single call to RemoveLocationUpdateCallback() is required to
-  // remove it.
-  virtual void AddLocationUpdateCallback(const LocationUpdateCallback& callback,
-                                         bool use_high_accuracy) = 0;
-
-  // Remove a previously registered observer. No-op if not previously registered
-  // via AddLocationUpdateCallback(). Returns true if the observer was removed.
-  virtual bool RemoveLocationUpdateCallback(
-      const LocationUpdateCallback& callback) = 0;
+  virtual scoped_ptr<Subscription> AddLocationUpdateCallback(
+      const LocationUpdateCallback& callback, bool use_high_accuracy) = 0;
 
   // Calling this method indicates the user has opted into using location
   // services, including sending network requests to [Google servers to] resolve
   // the user's location. Use this method carefully, in line with the rules in
   // go/chrome-privacy-doc.
   virtual void UserDidOptIntoLocationServices() = 0;
 
-  // Overrides the current location for testing. This function may be called on
-  // any thread. The completion callback will be invoked asynchronously on the
-  // calling thread when the override operation is completed.
+  // Overrides the current location for testing.
   //
-  // This function allows the current location to be faked without having to
-  // manually instantiate a GeolocationProvider backed by a MockLocationProvider
-  // that serves a fake location.
+  // Overrides the location for automation/testing. Suppresses any further
+  // updates from the actual providers and sends an update with the overridden
+  // position to all registered clients.
   //
   // Do not use this function in unit tests. The function instantiates the
   // singleton geolocation stack in the background and manipulates it to report
   // a fake location. Neither step can be undone, breaking unit test isolation
   // (crbug.com/125931).
-  static void OverrideLocationForTesting(
-      const Geoposition& position,
-      const base::Closure& completion_callback);
+  virtual void OverrideLocationForTesting(const Geoposition& position) = 0;
 
  protected:
   virtual~GeolocationProvider() {}
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_GEOLOCATION_PROVIDER_H_