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..45567d2fee9ef5e45c299dac1654a7f3a9b65780 100644
--- a/blimp/engine/mojo/blob_channel.mojom
+++ b/blimp/engine/mojo/blob_channel.mojom
@@ -4,11 +4,17 @@
 
 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 {
   // 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);
+  // 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