Makes use of EngineGeolocationFeature weak_ptr threadsafe.

blimp/engine/feature/geolocation/blimp_location_provider.h

Index: blimp/engine/feature/geolocation/blimp_location_provider.h
diff --git a/blimp/engine/feature/geolocation/blimp_location_provider.h b/blimp/engine/feature/geolocation/blimp_location_provider.h
index 39372da41c5dda1edc1d186653844ac6a5bce41c..a6a4c3a790bf17a9bdd1e3f3df0b344daa560010 100644
--- a/blimp/engine/feature/geolocation/blimp_location_provider.h
+++ b/blimp/engine/feature/geolocation/blimp_location_provider.h
@@ -17,11 +17,11 @@ namespace engine {
 class BlimpLocationProvider : public device::LocationProvider {
  public:
   // A delegate that implements a subset of LocationProvider's functions.
+  // All methods will be executed on |delegate_task_runner_|.
   class Delegate {
    public:
     using GeopositionReceivedCallback =
         base::Callback<void(const device::Geoposition&)>;
-
     virtual ~Delegate() {}
 
     virtual void RequestAccuracy(
@@ -31,7 +31,9 @@ class BlimpLocationProvider : public device::LocationProvider {
         const GeopositionReceivedCallback& callback) = 0;
   };
 
-  explicit BlimpLocationProvider(base::WeakPtr<Delegate> delegate);
+  BlimpLocationProvider(
+      base::WeakPtr<Delegate> delegate,
+      scoped_refptr<base::SequencedTaskRunner> delegate_task_runner);
   ~BlimpLocationProvider() override;
 
   // device::LocationProvider implementation.
@@ -42,15 +44,22 @@ class BlimpLocationProvider : public device::LocationProvider {
   void SetUpdateCallback(
       const LocationProviderUpdateCallback& callback) override;
 
+  void OnLocationUpdate(const device::Geoposition& geoposition);

[Wez, 2016/10/07 21:42:46]

This should be private, since it's an internal implementation detail of
BlimpLocationProvider.

Since you need to Bind() to it from the InvokeGeolocationCallback() function you
may need to move that function to be a static member, so it has visibility into
the private bit of the class.

[CJ, 2016/10/08 00:05:55]

Done.

+
  private:
   // This delegate handles a subset of the LocationProvider functionality.
   base::WeakPtr<Delegate> delegate_;
 
+  scoped_refptr<base::SequencedTaskRunner> delegate_task_runner_;
   device::Geoposition cached_position_;
 
   // True if a successful StartProvider call has occured.
   bool is_started_;
 
+  LocationProviderUpdateCallback location_update_callback_;
+
+  base::WeakPtrFactory<BlimpLocationProvider> weak_factory_;
+
   DISALLOW_COPY_AND_ASSIGN(BlimpLocationProvider);
 };