Adds GeolocationFeature for Blimp Geolocation project.

blimp/client/feature/geolocation_feature.h

Index: blimp/client/feature/geolocation_feature.h
diff --git a/blimp/client/feature/geolocation_feature.h b/blimp/client/feature/geolocation_feature.h
new file mode 100644
index 0000000000000000000000000000000000000000..0c5fa17c3d6bab738594bd880b1c607ce6c75e6a
--- /dev/null
+++ b/blimp/client/feature/geolocation_feature.h
@@ -0,0 +1,71 @@
+// Copyright 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_CLIENT_FEATURE_GEOLOCATION_FEATURE_H_
+#define BLIMP_CLIENT_FEATURE_GEOLOCATION_FEATURE_H_
+
+#include <memory>
+
+#include "blimp/common/proto/geolocation.pb.h"
+#include "blimp/net/blimp_message_processor.h"
+#include "content/public/common/geoposition.h"
+
+namespace blimp {
+namespace client {
+
+// Client-side feature handling geolocation messages.
+class GeolocationFeature : public BlimpMessageProcessor {
+ public:
+  // A delegate to be notified of specific geolocation events, such as
+  // change of interest in geolocation updates.
+  class GeolocationFeatureDelegate {

[Wez, 2016/07/22 01:35:08]

Why does the GeolocationFeature need its own Delegate interface, rather than
just working with a LocationProvider directly?

[CJ, 2016/07/22 19:22:35]

At this point in time it is not planned to work with a LocationProvider
directly. The original plan was to have some class to handle bridging the gap
between the GeolocationProviderImpl and the GeolocationFeature. If it makes
sense for that to be a LocationProvider, I'll be happy to refactor it to be so. 

[Wez, 2016/07/22 22:14:51]

I would recommend having GeolocationFeature instantiated with a LocationProvider
to use, rather than adding another intermediate layer of glue, I think - the
glue layer would be so trivial as to not really be worth it, IMO!

Using LocationProvider would also mean that you could move OnLocationUpdate to
be an implementation detail (you'd Bind() it to create the callback to pass to
the LocationProvider), and you can remove SetDelegate and just pass the
LocationProvider as a constructor parameter.

+   public:
+    // Handles updates in accuracy level of the listen state.
+    virtual void OnGeolocationInterestUpdate(
+        GeolocationSetInterestLevelMessage::Level level) = 0;
+
+    // Called when a refresh in geolocation data is needed.
+    virtual void OnRequestRefresh() = 0;
+  };
+
+  GeolocationFeature();
+  ~GeolocationFeature() override;
+
+  // Sets the BlimpMessageProcessor that will be used to send
+  // BlimpMessage::GEOLOCATION messages to the engine.
+  void set_outgoing_message_processor(
+      std::unique_ptr<BlimpMessageProcessor> processor);
+
+  // Sets a GeolocationFeatureDelegate to be notified of all geolocation
+  // updates from the engine.
+  void SetDelegate(GeolocationFeatureDelegate* delegate);

[Wez, 2016/07/22 01:35:08]

You're passing in a bare-pointer, so be clear about the ownership/lifetime
expectations of |delegate|

[CJ, 2016/07/22 19:22:35]

Made it into a unique_ptr handled by the GeolocationFeature

+
+  // Sends engine an update of the client's geoposition.
+  void OnLocationUpdate(const content::Geoposition& position);
+
+  // BlimpMessageProcessor implementation.
+  void ProcessMessage(std::unique_ptr<BlimpMessage> message,
+                      const net::CompletionCallback& callback) override;
+
+ private:
+  // Creates a GeolocationPositionMessage that reflects the given
+  // geoposition and sends it to the engine.
+  void SendGeolocationPositionMessage(const content::Geoposition& position);
+
+  // Creates a GeolocationErrorMessage that reflects the error defined
+  // in the given geoposition and sends it.
+  void SendGeolocationErrorMessage(const content::Geoposition& position);

[Wez, 2016/07/22 01:35:08]

nit: I'd suggest having this accept the error_code field from a Geoposition,
rather than a whole Geoposition, for clarity (otherwise it's not clear what the
function expects the other fields to be!)

[CJ, 2016/07/22 19:22:35]

Done.

+
+  GeolocationFeatureDelegate* delegate_ = nullptr;
+
+  // Used to send BlimpMessage::GEOLOCATION message to the engine.
+  std::unique_ptr<BlimpMessageProcessor> outgoing_message_processor_;
+
+  DISALLOW_COPY_AND_ASSIGN(GeolocationFeature);
+};
+
+}  // namespace client
+}  // namespace blimp
+
+#endif  // BLIMP_CLIENT_FEATURE_GEOLOCATION_FEATURE_H_