Add Mojo IPC for seeding new Renderer with Browser's cached blob state.

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;
 
 // Exposes BlobChannel data producer methods to the renderer processes.
 // The renderer can use this service to push bulk data such as images to
 // the client.
 interface BlobChannel {
+  // Gets the list of cached BlobIDs and their replication status in the
+  // browser process' BlobCache. The replication status is represented
+  // as a boolean which, when true, indicates that the blob has been
+  // sent to the client.
+  // TODO(kmarshall): Add a delegate receiver to process cache invalidation
+  // events from the browser as they occur.
+  GetCachedBlobIds() => (map<string, bool> cache_state);
+
   // Stores the blob |id| in the BlobCache.
   // Because the IPC channel is a shared resource and payloads can be quite
   // large, we use shared memory to reduce channel contention and associated
   // latency with other components/features.
   //
   // The buffer is released when the callee discards the handle for |data|.
   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);
 };