Add module annotation to specify the name of the java class for constants.

mojo/public/interfaces/bindings/tests/sample_interfaces.mojom

 // Copyright 2014 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.
 
 [JavaPackage="org.chromium.mojo.bindings.test.sample",
+ JavaConstantsClassName="InterfaceConstants",
  Foo = "hello world"]
 module sample {
 
+const uint64 kLong = 4405;
+
 enum Enum {
   ENUM_VALUE
 };
 
 [Client=ProviderClient]
 interface Provider {
   EchoString(string a) => (string a);
   EchoStrings(string a, string b) => (string a, string b);
   EchoMessagePipeHandle(handle<message_pipe> a) => (handle<message_pipe> a);
   EchoEnum(Enum a) => (Enum a);
 };
 
 // TODO(darin): We shouldn't need this, but JS bindings don't work without it.
 interface ProviderClient {
 };
 
 }