Blimp: Add BlobChannel Helium messages and delegate impls.

blimp/common/proto/blob_channel.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.
 
 syntax = "proto2";
 
 option optimize_for = LITE_RUNTIME;
 
-package cc.proto;
+package blimp;
 
-message Vector2d {
-  optional int64 x = 1;
-  optional int64 y = 2;
+message TransferBlob {
+  optional string blob_id = 1;
+  optional bytes payload = 2;
 }
+
+message BlobChannelMessage {
+  oneof type {
+    // Engine => Client types.
+    TransferBlob transfer_blob = 1;
+  }
+}