Blimp: Add BlobChannel Helium messages and delegate impls.

blimp/common/proto/blob_channel.proto

Index: blimp/common/proto/blob_channel.proto
diff --git a/blimp/common/proto/blob_channel.proto b/blimp/common/proto/blob_channel.proto
new file mode 100644
index 0000000000000000000000000000000000000000..50c5c76f4541d725ab5b1c3911a35c6e625340b9
--- /dev/null
+++ b/blimp/common/proto/blob_channel.proto
@@ -0,0 +1,22 @@
+// 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 blimp;
+
+message BlobChannelMessage {
+  enum Type {
+    UNKNOWN = 0;
+
+    // Engine => Client types.
+    TRANSFER_BLOB = 1;
+  }
+
+  optional Type type = 1 [default = UNKNOWN];
+  optional string blob_id = 2;
+  optional bytes payload = 3;
+}