Blimp: Add BlobChannel Helium messages and delegate impls.

blimp/common/proto/blob_channel.proto

Index: blimp/common/proto/blob_channel.proto
diff --git a/cc/proto/vector2d.proto b/blimp/common/proto/blob_channel.proto
similarity index 51%
copy from cc/proto/vector2d.proto
copy to blimp/common/proto/blob_channel.proto
index 15171844ffc443d28cae7c70e2149ac3989200ab..0f862f71cb2e426f8f6a2d3f156b1cc94b219201 100644
--- a/cc/proto/vector2d.proto
+++ b/blimp/common/proto/blob_channel.proto
@@ -6,9 +6,16 @@ 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;
+  }
 }