Split ExtensionMessageFilter up into a UI thread part and an IO thread part.

extensions/browser/io_thread_extension_message_filter.h

+// Copyright 2015 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 EXTENSIONS_BROWSER_IO_THREAD_EXTENSION_MESSAGE_FILTER_H_
+#define EXTENSIONS_BROWSER_IO_THREAD_EXTENSION_MESSAGE_FILTER_H_
+
+#include "base/compiler_specific.h"
+#include "base/macros.h"
+#include "base/memory/weak_ptr.h"
+#include "content/public/browser/browser_message_filter.h"
+
+struct ExtensionHostMsg_Request_Params;
+
+namespace content {
+class BrowserContext;
+}
+
+namespace extensions {
+
+class InfoMap;
+
+// This class filters out incoming extension-specific IPC messages from the
+// renderer process. It is created on the UI thread, but handles messages on the
+// IO thread and is destroyed there.
+class IOThreadExtensionMessageFilter : public content::BrowserMessageFilter {
+ public:
+  IOThreadExtensionMessageFilter(int render_process_id,
+                                 content::BrowserContext* context);
+
+  int render_process_id() { return render_process_id_; }

[not at google - send to devlin, 2015/02/10 18:37:15]

Where is this called from?

[Bernhard Bauer, 2015/02/10 19:02:34]

WebRequestInternalAddEventListenerFunction::RunSync(). This is also the reason
why we can't just hand out a WeakPtr<IPC::Sender>, but have to expose the full
class :-/

+
+ private:
+  friend class base::DeleteHelper<IOThreadExtensionMessageFilter>;
+  friend class content::BrowserThread;
+
+  ~IOThreadExtensionMessageFilter() override;
+
+  // content::BrowserMessageFilter implementation.
+  void OnDestruct() const override;
+  bool OnMessageReceived(const IPC::Message& message) override;
+
+  // Message handlers on the IO thread.
+  void OnExtensionGenerateUniqueID(int* unique_id);
+  void OnExtensionResumeRequests(int route_id);
+  void OnExtensionRequestForIOThread(
+      int routing_id,
+      const ExtensionHostMsg_Request_Params& params);
+
+  const int render_process_id_;
+
+  // The browser context as a void pointer, for use as an identifier on the IO
+  // thread.
+  void* browser_context_id_;
+
+  scoped_refptr<extensions::InfoMap> extension_info_map_;
+
+  // Weak pointers produced by this factory are bound to the IO thread.
+  base::WeakPtrFactory<IOThreadExtensionMessageFilter> weak_ptr_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(IOThreadExtensionMessageFilter);
+};
+
+}  // namespace extensions
+
+#endif  // EXTENSIONS_BROWSER_IO_THREAD_EXTENSION_MESSAGE_FILTER_H_