Add ChildMessageFilter, a base class for renderer/worker cross-thread MessageFilter

content/child/child_message_filter.h

Index: content/child/child_message_filter.h
diff --git a/content/child/child_message_filter.h b/content/child/child_message_filter.h
new file mode 100644
index 0000000000000000000000000000000000000000..21cccac065a9a81b3f3f7c4e36ca70b6eda6b8a0
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+++ b/content/child/child_message_filter.h
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+// Copyright 2013 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 CONTENT_CHILD_CROSS_MESSAGE_FILTER_H_
+#define CONTENT_CHILD_CROSS_MESSAGE_FILTER_H_
+
+#include "ipc/ipc_channel_proxy.h"
+
+namespace base {
+class TaskRunner;
+}
+
+namespace content {
+
+class ThreadSafeSender;
+
+// A base class for implementing IPC MessageFilter's that run on a different
+// thread or TaskRunner than the main thread.
+class ChildMessageFilter
+    : public base::RefCountedThreadSafe<ChildMessageFilter>,
+      public IPC::Sender {
+ public:
+  // IPC::Sender implementation. Can be called on any threads.
+  virtual bool Send(IPC::Message* message) OVERRIDE;
+
+  // If implementers want to run OnMessageReceived on a different task
+  // runner it should override this and return the TaskRunner for the message.
+  // Returning NULL runs OnMessageReceived() on the current IPC thread.
+  virtual base::TaskRunner* OverrideTaskRunnerForMessage(
+      const IPC::Message& msg) = 0;
+
+  // If OverrideTaskRunnerForMessage is overriden and returns non-null
+  // this will be called on the returned TaskRunner.
+  virtual bool OnMessageReceived(const IPC::Message& msg) = 0;
+
+  // This method is called when WorkerTaskRunner::PostTask() returned false
+  // for the target thread.  Note that there's still a little chance that
+  // PostTask() returns true but OnMessageReceived() is never called on the
+  // target thread.  By default this does nothing.
+  virtual void OnStaleMessageReceived(const IPC::Message& msg) {}
+
+ protected:
+  ChildMessageFilter();
+  virtual ~ChildMessageFilter();
+
+ private:
+  class Internal;
+  friend class ChildThread;
+  friend class RenderThreadImpl;
+  friend class WorkerThread;
+
+  friend class base::RefCountedThreadSafe<ChildMessageFilter>;
+
+  IPC::ChannelProxy::MessageFilter* GetFilter();
+
+  // This implements IPC::ChannelProxy::MessageFilter to hide the actual
+  // filter methods from child classes.
+  Internal* internal_;
+
+  scoped_refptr<ThreadSafeSender> thread_safe_sender_;
+
+  DISALLOW_COPY_AND_ASSIGN(ChildMessageFilter);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_CHILD_CROSS_MESSAGE_FILTER_H_