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..a1a7c1587d43162c149d69ba47fb6a5383d454d1 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 = 2;

[Wez, 2016/05/24 01:18:40]

nit: You don't think blob_id is likely to be common w/ other messages?

[Kevin M, 2016/05/25 00:06:33]

I was thinking I could make promote it provided that it makes sense for the use
case. For get, we might want to specify multiple IDs at once. Cache digest
upload would use multiple IDs or some kind of efficiently packed digest/Bloom
filter.

[Wez, 2016/05/25 02:47:44]

Acknowledged.

+  optional bytes payload = 1;
+}
+
+message BlobChannelMessage {
+  oneof type {
+    // Engine => Client types.
+    TransferBlob transfer_blob = 1;
+  }
 }