Adding a router class to handle messages that expect responses.

mojo/bindings/java/src/org/chromium/mojo/bindings/Struct.java

Index: mojo/bindings/java/src/org/chromium/mojo/bindings/Struct.java
diff --git a/mojo/bindings/java/src/org/chromium/mojo/bindings/Struct.java b/mojo/bindings/java/src/org/chromium/mojo/bindings/Struct.java
index f7c16a2decb0fa75c54e0684ed020a1b6bfa9163..c1dd59fdd781deaf6a5806071a48ed23aa7cedb1 100644
--- a/mojo/bindings/java/src/org/chromium/mojo/bindings/Struct.java
+++ b/mojo/bindings/java/src/org/chromium/mojo/bindings/Struct.java
@@ -73,4 +73,18 @@ public abstract class Struct {
         return encoder.getMessage();
     }
 
+    /**
+     * Returns the serialization of the struct prepended with the given header.
+     *
+     * @param header the header to prepend to the returned message.
+     * @param core the |Core| implementation used to generate handles. Only used if the |Struct|
+     *            being encoded contains interfaces, can be |null| otherwise.
+     */
+    public Message serializeWithHeader(Core core, MessageHeader header) {
+        Encoder encoder = new Encoder(core, mEncodedBaseSize + header.getSize());
+        header.encode(encoder);
+        encode(encoder);
+        return encoder.getMessage();
+    }
+
 }