Adds EngineGeolocationFeature for Blimp Geolocation project.

blimp/engine/feature/geolocation/engine_geolocation_feature.h

Index: blimp/engine/feature/geolocation/engine_geolocation_feature.h
diff --git a/blimp/engine/feature/geolocation/engine_geolocation_feature.h b/blimp/engine/feature/geolocation/engine_geolocation_feature.h
new file mode 100644
index 0000000000000000000000000000000000000000..bd0ef390cfe5bee461c8ac5e0c3d2471f3f1ab26
--- /dev/null
+++ b/blimp/engine/feature/geolocation/engine_geolocation_feature.h
@@ -0,0 +1,62 @@
+// 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_ENGINE_FEATURE_GEOLOCATION_ENGINE_GEOLOCATION_FEATURE_H_
+#define BLIMP_ENGINE_FEATURE_GEOLOCATION_ENGINE_GEOLOCATION_FEATURE_H_
+
+#include "blimp/net/blimp_message_processor.h"
+#include "content/public/common/geoposition.h"
+
+namespace blimp {
+namespace engine {
+
+// Handles all incoming and outgoing protobuf messages types tied to
+// geolocation. Delegates can be added to be notified of incoming

[Kevin M, 2016/06/27 16:57:41]

Can you rephrase the last sentence to use the active voice instead of the
passive voice?

[CJ, 2016/06/27 22:04:27]

Done.

+// messages.
+class EngineGeolocationFeature : public BlimpMessageProcessor {
+ public:
+  // A delegate to be notified of geolocation related incoming events.
+  class GeolocationMessageDelegate {

[Kevin M, 2016/06/27 16:57:42]

"Delegate" is fine here, since all references to this class are unambiguous
anyways ("EngineGeolocationFeature::Delegate")

[CJ, 2016/06/27 22:04:27]

Done.

+   public:
+    // Called when the client is sending a Geolocation to the Engine.
+    // May also encapsulate an ErrorCode, to be passed through to the
+    // JavaScript.
+    virtual void OnLocationResponse(const content::Geoposition& position);

[Kevin M, 2016/06/27 16:57:41]

Make this pure virtual?

[CJ, 2016/06/27 22:04:26]

Done.

+  };
+
+  ~EngineGeolocationFeature() override;
+
+  void set_geolocation_message_sender(

[Kevin M, 2016/06/27 16:57:41]

nit: I think we've been calling it "outgoing_message_processor"? Not a big fan
of that though, since the "sender" terminology has had more traction... (seems
like a job for a fixit CL)

Regardless, let's use feature-agnostic terminology for these types of common
operations.

[CJ, 2016/06/27 22:04:27]

I was following the pattern found here:
https://cs.chromium.org/chromium/src/blimp/engine/feature/engine_render_widge...

I havent really seen the outgoing_message_processor variable. 

I'm happy either way. Let me know what you think.

[Kevin M, 2016/06/28 01:14:38]

Yeah, it needs fixin'. Use outgoing_message_processor for now and we'll address
it later. Maybe file a bug to standardize the variable & getter names?

[CJ, 2016/06/29 00:12:12]

Done.

+      std::unique_ptr<BlimpMessageProcessor> message_processor);
+
+  // Notifies the client that the is listening engine is listening for
+  // geoposition information with the given accuracy.
+  void SendUpdateListenStateMessage(bool enable_high_accuracy);

[Kevin M, 2016/06/27 16:57:42]

Who's supposed to call these methods? Does it make sense to have them be public?

[CJ, 2016/06/27 22:04:27]

BlimpLocationProvider would call this through it's RequestRefresh() function. 

[Kevin M, 2016/06/28 01:14:38]

I think that we should probably invert that relationship. Features are clients
of platform code, not the other way around.

So, BlimpLocationProvider calls BlimpLocationProvider::Delegate methods, of
which EngineGeolocationFeature is an impl class.

[CJ, 2016/06/29 00:12:12]

Done.

+
+  // Notifies the client that the engine is no long listening for updates.

[Kevin M, 2016/06/27 16:57:41]

typo: longer

[CJ, 2016/06/27 22:04:27]

Done.

+  void SendStopListenStateMessage();
+
+  // Notifies the client that an update in geoposition is needed as soon

[Kevin M, 2016/06/27 16:57:41]

suggestion: Requests an updated geoposition from the client.

[CJ, 2016/06/27 22:04:27]

Done.

+  // as possible.
+  void SendRequestRefreshMessage();
+
+  void SetDelegate(GeolocationMessageDelegate* delegate);
+
+  // BlimpMessageProcessor implementation.
+  void ProcessMessage(std::unique_ptr<BlimpMessage> message,
+                      const net::CompletionCallback& callback) override;
+
+ private:
+  GeolocationMessageDelegate* delegate_;

[Kevin M, 2016/06/27 16:57:41]

= nullptr;

[CJ, 2016/06/27 22:04:27]

Done.

+  std::unique_ptr<BlimpMessageProcessor> geolocation_message_sender_;
+
+  void UpdateGeolocation(content::Geoposition* geoposition);
+
+  DISALLOW_COPY_AND_ASSIGN(EngineGeolocationFeature);
+};
+
+}  // namespace engine
+}  // namespace blimp
+
+#endif  // BLIMP_ENGINE_FEATURE_GEOLOCATION_ENGINE_GEOLOCATION_FEATURE_H_