[Blimp] Adds Blimp EngineSession and ClientSession skeleton

blimp/common/proto/client_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 client-originating browser control messages.
 //
 // Current definitions are just placeholders and are NOT final.
 // Feel free to modify this interface as necessary during feature work.
 
 syntax = "proto2";
 
 option optimize_for = LITE_RUNTIME;
 
 message NavigateArgs {
   optional string url = 1;
 }
 
 message ClientControlMessage {
   enum Type {
     NAVIGATE = 1;
     STOP = 2;
     RELOAD = 3;
     BACK = 4;
     FORWARD = 5;
+    NEW_TAB = 6;
+    CLOSE_TAB = 7;
   }
   optional Type type = 1;
 
   optional NavigateArgs navigate = 1000;
 }