Use shared memory for moving data over BlobChannel Mojo interface.

blimp/engine/mojo/blob_channel.mojom

Index: blimp/engine/mojo/blob_channel.mojom
diff --git a/blimp/engine/mojo/blob_channel.mojom b/blimp/engine/mojo/blob_channel.mojom
index 0960916fea10655f4e3511b8e2c1684108c08ace..9f1fafee872df05d6cbf3bc8dff1f6807829814b 100644
--- a/blimp/engine/mojo/blob_channel.mojom
+++ b/blimp/engine/mojo/blob_channel.mojom
@@ -6,9 +6,8 @@ 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