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..e8916ea7e5662031d1595db9f15fb5e4f44103d4
--- /dev/null
+++ b/blimp/client/feature/geolocation_feature.h
@@ -0,0 +1,76 @@
+// 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 <string>
+
+#include "blimp/common/proto/geolocation.pb.h"
+#include "blimp/net/blimp_message_processor.h"
+#include "device/geolocation/geoposition.h"
+#include "device/geolocation/location_provider.h"
+
+namespace blimp {
+namespace client {
+
+// Client-side feature handling geolocation messages.
+class GeolocationFeature : public BlimpMessageProcessor {
+ public:
+  // |location_provider| will be the only LocationProvider the

[Kevin M, 2016/08/15 20:35:40]

Nit: I think this is already implied by the fact that we don't have
post-construction setters for this type.

[CJ, 2016/08/15 21:59:32]

Done.

+  // GeolocationFeature will gather information from.
+  explicit GeolocationFeature(
+      std::unique_ptr<device::LocationProvider> location_provider);
+  ~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);
+
+  // BlimpMessageProcessor implementation.
+  void ProcessMessage(std::unique_ptr<BlimpMessage> message,
+                      const net::CompletionCallback& callback) override;
+
+ private:
+  // Sends engine an update of the client's geoposition.
+  void OnLocationUpdate(const device::LocationProvider* location_provider,
+                        const device::Geoposition& position);
+
+  // Communicates to the client a change of interest level from the engine.
+  void SetInterestLevel(GeolocationSetInterestLevelMessage::Level level);
+
+  // Creates a GeolocationPositionMessage that reflects the given
+  // geoposition and sends it to the engine.
+  void SendGeolocationPositionMessage(const device::Geoposition& position);
+
+  // Creates a GeolocationErrorMessage that reflects the error defined
+  // in the given geoposition and sends it.
+  void SendGeolocationErrorMessage(
+      const GeolocationErrorMessage::ErrorCode& error_code,

[Kevin M, 2016/08/15 20:35:40]

ErrorCode is a POD type, so should be passed as-is and not as a reference.

[CJ, 2016/08/15 21:59:32]

POD?

+      const std::string& error_message);
+
+  // Callback function when message finishes sending.
+  void OnSendComplete(int result);
+
+  // Used to obtain the client's location.
+  std::unique_ptr<device::LocationProvider> location_provider_;
+
+  // Used to send BlimpMessage::GEOLOCATION message to the engine.
+  std::unique_ptr<BlimpMessageProcessor> outgoing_message_processor_;
+
+  // Run when message is finished sending.
+  net::CompletionCallback completion_callback_;
+
+  // True if a message is not in the process of being sent.

[Kevin M, 2016/08/15 20:35:40]

I think the meaning of this variable, and how it is used, would be easier to
comprehend if we inverted the semantics. For example, it could be "send_active_"
which starts out as false, becomes true when a message is being sent, then false
again once the message is delivered.

[CJ, 2016/08/15 21:59:32]

Done.

+  bool can_send_message_ = true;
+
+  DISALLOW_COPY_AND_ASSIGN(GeolocationFeature);
+};
+
+}  // namespace client
+}  // namespace blimp
+
+#endif  // BLIMP_CLIENT_FEATURE_GEOLOCATION_FEATURE_H_