[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;
-  }
-  optional Type type = 1;
-
-  optional NavigateArgs navigate = 1000;
-}