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..10065ed73538eb4f14aadb584601fb5c2e3f4278 100644
--- a/blimp/engine/mojo/blob_channel.mojom
+++ b/blimp/engine/mojo/blob_channel.mojom
@@ -5,10 +5,10 @@
 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);
+  // Stores the blob |id| in the BlobCache, using shared memory to keep
+  // large data payloads out of the Mojo IPC channel.
+  // 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