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diff --git a/content/renderer/pepper/pepper_hung_plugin_filter.h b/content/renderer/pepper/pepper_hung_plugin_filter.h
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+++ b/content/renderer/pepper/pepper_hung_plugin_filter.h
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+// 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 CONTENT_RENDERER_PEPPER_PEPPER_HUNG_PLUGIN_FILTER_H_
+#define CONTENT_RENDERER_PEPPER_PEPPER_HUNG_PLUGIN_FILTER_H_
+
+#include "base/file_path.h"
+#include "base/memory/ref_counted.h"
+#include "base/message_loop_proxy.h"
+#include "base/synchronization/lock.h"
+#include "ipc/ipc_channel_proxy.h"
+#include "ipc/ipc_sync_message_filter.h"
+#include "ppapi/proxy/host_dispatcher.h"
+
+namespace content {
+
+// This class monitors a renderer <-> pepper plugin channel on the I/O thread
+// of the renderer for a hung plugin.
+//
+// If the plugin is not responding to sync messages, it will notify the browser
+// process and give the user the option to kill the hung plugin.
+//
+// Note that this class must be threadsafe since it will get the begin/end
+// block notifications on the main thread, but the filter is run on the I/O
+// thread. This is important since when we're blocked on a sync message to a
+// hung plugin, the main thread is frozen.
+//
+// NOTE: This class is refcounted (via SyncMessageStatusReceiver).
+class PepperHungPluginFilter
+    : public ppapi::proxy::HostDispatcher::SyncMessageStatusReceiver {
+ public:
+  // The |view_routing_id| is the ID of the render_view so that this class can
+  // send messages to the browser via that view's route. The |plugin_child_id|
+  // is the ID in the browser process of the pepper plugin process host. We use
+  // this to identify the proper plugin process to terminate.
+  PepperHungPluginFilter(const FilePath& plugin_path,
+                         int view_routing_id,
+                         int plugin_child_id);
+  virtual ~PepperHungPluginFilter();
+
+  // SyncMessageStatusReceiver implementation.
+  virtual void BeginBlockOnSyncMessage() OVERRIDE;
+  virtual void EndBlockOnSyncMessage() OVERRIDE;
+
+  // MessageFilter implementation.
+  virtual void OnFilterAdded(IPC::Channel* channel) OVERRIDE;
+  virtual void OnFilterRemoved() OVERRIDE;
+  virtual void OnChannelError() OVERRIDE;
+  virtual bool OnMessageReceived(const IPC::Message& message) OVERRIDE;
+
+ private:
+  // Makes sure that the hung timer is scheduled.
+  void EnsureTimerScheduled();
+
+  // Checks whether the plugin could have transitioned from hung to unhung and
+  // notifies the browser if so.
+  void MayHaveBecomeUnhung();
+
+  // Checks if the plugin is considered hung based on whether it has been
+  // blocked for long enough.
+  bool IsHung() const;
+
+  // Timer handler that checks for a hang after a timeout.
+  void OnHangTimer();
+
+  // Sends the hung/unhung message to the browser process.
+  void SendHungMessage(bool is_hung);
+
+  base::Lock lock_;
+
+  FilePath plugin_path_;
+  int view_routing_id_;
+  int plugin_child_id_;
+
+  // Used to post messages to the renderer <-> browser message channel from
+  // other threads without having to worry about the lifetime of that object.
+  // We don't actually use the "sync" feature of this filter.
+  scoped_refptr<IPC::SyncMessageFilter> filter_;
+
+  scoped_refptr<base::MessageLoopProxy> io_loop_;
+
+  // The time when we start being blocked on a sync message. If there are
+  // nested ones, this is the time of the outermost one.
+  //
+  // This will be is_null() if we've never blocked.
+  base::TimeTicks began_blocking_time_;
+
+  // Time that the last message was received from the plugin.
+  //
+  // This will be is_null() if we've never received any messages.
+  base::TimeTicks last_message_received_;
+
+  // Number of nested sync messages that we're blocked on.
+  int pending_sync_message_count_;
+
+  // True when we've sent the "plugin is hung" message to the browser. We track
+  // this so we know to look for it becoming unhung and send the corresponding
+  // message to the browser.
+  bool hung_plugin_showing_;
+
+  bool timer_task_pending_;
+
+  DISALLOW_COPY_AND_ASSIGN(PepperHungPluginFilter);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_RENDERER_PEPPER_PEPPER_HUNG_PLUGIN_FILTER_H_