Makes use of EngineGeolocationFeature weak_ptr threadsafe.

blimp/engine/feature/geolocation/blimp_location_provider.h

 // Copyright (c) 2016 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 BLIMP_ENGINE_FEATURE_GEOLOCATION_BLIMP_LOCATION_PROVIDER_H_
 #define BLIMP_ENGINE_FEATURE_GEOLOCATION_BLIMP_LOCATION_PROVIDER_H_
 
 #include "base/memory/weak_ptr.h"
 #include "blimp/common/proto/geolocation.pb.h"
 #include "device/geolocation/geoposition.h"
 #include "device/geolocation/location_provider.h"
 
 namespace blimp {
 namespace engine {
 
 // Location provider for Blimp using the device's provider over the network.

[Kevin M, 2016/09/09 17:07:04]

Add good comments about threading requirements here - about
BlimpLocationProvider and Delegate.

[CJ, 2016/09/09 19:52:41]

Done.

 class BlimpLocationProvider : public device::LocationProvider {
  public:
   // A delegate that implements a subset of LocationProvider's functions.

[Kevin M, 2016/09/09 17:07:04]

Also document that all methods will be executed on |delegate_task_runner_|.

[CJ, 2016/09/09 19:52:41]

Done.

   class Delegate {
    public:
     using GeopositionReceivedCallback =
         base::Callback<void(const device::Geoposition&)>;
 
     virtual ~Delegate() {}
 
     virtual void RequestAccuracy(
         GeolocationSetInterestLevelMessage::Level level) = 0;
     virtual void OnPermissionGranted() = 0;
     virtual void SetUpdateCallback(
+        scoped_refptr<base::SingleThreadTaskRunner> caller_task_runner,
         const GeopositionReceivedCallback& callback) = 0;
   };
 
-  explicit BlimpLocationProvider(base::WeakPtr<Delegate> delegate);
+  BlimpLocationProvider(
+      base::WeakPtr<Delegate> delegate,
+      scoped_refptr<base::SingleThreadTaskRunner> delegate_task_runner);
   ~BlimpLocationProvider() override;
 
   // device::LocationProvider implementation.
   bool StartProvider(bool high_accuracy) override;
   void StopProvider() override;
   const device::Geoposition& GetPosition() override;
   void OnPermissionGranted() override;
   void SetUpdateCallback(
       const LocationProviderUpdateCallback& callback) override;
 
  private:
   // This delegate handles a subset of the LocationProvider functionality.
   base::WeakPtr<Delegate> delegate_;
 
+  scoped_refptr<base::SingleThreadTaskRunner> delegate_task_runner_;
+
   device::Geoposition cached_position_;
 
   // True if a successful StartProvider call has occured.
   bool is_started_;
 
   DISALLOW_COPY_AND_ASSIGN(BlimpLocationProvider);
 };
 
 }  // namespace engine
 }  // namespace blimp
 
 #endif  // BLIMP_ENGINE_FEATURE_GEOLOCATION_BLIMP_LOCATION_PROVIDER_H_