Use shared memory for moving data over BlobChannel Mojo interface.

blimp/engine/mojo/blob_channel.mojom

 // 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.
 
 module blimp.engine.mojom;
 
 interface BlobChannel {
   // Stores the blob |id| in the BlobCache.
-  // TODO(kmarshall): Use shared memory for more efficient data transfer, see
-  // crbug.com/614564 .
-  PutBlob(string id, string data);
+  // The service invokes the no-arg callback after the operation has completed.
+  PutBlob(string id, handle<shared_buffer> data, uint32 size) => ();
 
   // Requests that the BlobChannel push the blob |id| over the wire.
   // The request will be ignored if the BlobChannel knows that
   // the client already has the data.
   DeliverBlob(string id);
 };