Introduce MessageFilterHost for Pepper ResourceHosts.

ppapi/host/message_filter_host.h

Index: ppapi/host/message_filter_host.h
diff --git a/ppapi/host/message_filter_host.h b/ppapi/host/message_filter_host.h
new file mode 100644
index 0000000000000000000000000000000000000000..9aa1c5bbaa41066f4e918affd34e14f713a605a9
--- /dev/null
+++ b/ppapi/host/message_filter_host.h
@@ -0,0 +1,38 @@
+// Copyright (c) 2012 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.
+
+#ifndef PPAPI_HOST_MESSAGE_FILTER_HOST_H_
+#define PPAPI_HOST_MESSAGE_FILTER_HOST_H_
+
+#include "base/compiler_specific.h"
+#include "base/memory/ref_counted.h"
+#include "ppapi/host/ppapi_host_export.h"
+#include "ppapi/host/resource_host.h"
+
+namespace ppapi {
+namespace host {
+
+class PpapiHost;
+class ResourceMessageFilter;
+
+// This class is a generic ResourceHost that is composed of a single
+// ResourceMessageFilter. There are cases where ResourceHosts only serve the
+// purpose of passing messages onto a message filter to be handled on another
+// thread. This class can be used as the host in those cases.
+class PPAPI_HOST_EXPORT MessageFilterHost : public ResourceHost {
+ public:
+  MessageFilterHost(PpapiHost* host,
+                    PP_Instance instance,
+                    PP_Resource resource,
+                    const scoped_refptr<ResourceMessageFilter>& message_filter);
+  virtual ~MessageFilterHost();
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(MessageFilterHost);
+};
+
+}  // namespace host
+}  // namespace ppapi
+
+#endif  // PPAPI_HOST_MESSAGE_FILTER_HOST_H_