Adds EngineGeolocationFeature for Blimp Geolocation project.

blimp/common/proto/tab_control.proto

 // Copyright 2015 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 browser tab control messages.
 
 syntax = "proto2";
 
 option optimize_for = LITE_RUNTIME;
 
+import "common.proto";
+
 package blimp;
 
 // Contains display information that represents resize events coming from the
 // client device.
 message SizeMessage {
   optional uint64 width = 1;
   optional uint64 height = 2;
   optional float device_pixel_ratio = 3;
 }
 
-message EmptyMessage {}
-
 message TabControlMessage {
   // Feature-specific messages follow.
   oneof tab_control {
     // Client <=> Server types.
     EmptyMessage create_tab = 40;
     EmptyMessage close_tab = 41;
 
     // Client => Server types.
     SizeMessage size = 42;
   }
 }