Adds EngineGeolocationFeature for Blimp Geolocation project.

blimp/common/proto/geolocation.proto

+// 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.
+//
+// Message definitions for geolocation messages.
+
+syntax = "proto2";
+
+option optimize_for = LITE_RUNTIME;
+
+import "tab_control.proto";

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

Promote EmptyMessage to a "common.proto" file - this dependency is confusing
otherwise.

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

Good idea. Done.

+
+package blimp;
+
+message ErrorMessage {
+  // These values follow the W3C geolocation specification and can be returned

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

Add a link to the specification?

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

Done.

+  // to JavaScript without the need for a conversion.
+  enum ErrorCode {
+    option allow_alias = true;
+    ERROR_CODE_NONE = 0;
+    ERROR_CODE_PERMISSION_DENIED = 1;
+    ERROR_CODE_POSITION_UNAVAILABLE = 2;
+    ERROR_CODE_TIMEOUT = 3;
+    ERROR_CODE_LAST = 3;
+  }
+
+  optional ErrorCode error_code = 1;
+  optional string error_message = 2;
+}
+
+message LocationMessage {
+  // Please refer to content/public/common/geoposition.h for explanation of

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

nit: "please" is optional - one-liner comments are generally more declarative
than polite

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

Done.

+  // these fields and associated units.
+  optional double latitude = 1;
+  optional double longitude = 2;
+  optional double altitude = 3;
+  optional double accuracy = 4;
+  optional double altitude_accuracy = 5;
+  optional double heading = 6;
+  optional double speed = 7;
+  optional int64 timestamp_millis = 8;
+}
+
+message UpdateListenStateMessage {
+  enum ListenState {
+    ACCURACY_HIGH = 0;
+    ACCURACY_LOW = 1;
+    STOPPED = 2;
+  }
+
+  optional ListenState listen_state = 1;
+}
+
+message GeolocationMessage {
+  oneof type {
+    // Server => Client types.
+    UpdateListenStateMessage update_listen_state = 1;
+    EmptyMessage request_refresh = 2;
+
+    // Client => Server types.
+    LocationMessage location = 3;
+    ErrorMessage error = 4;
+  }
+}