Decouple IPC::MessageFilter from IPC::Channel

content/public/browser/browser_message_filter.h

Index: content/public/browser/browser_message_filter.h
diff --git a/content/public/browser/browser_message_filter.h b/content/public/browser/browser_message_filter.h
index f1334b941c0c7779692a527799eaa5b97df4c3f8..a04ef95dc9cdb6e5f3f2043731576600daed7df8 100644
--- a/content/public/browser/browser_message_filter.h
+++ b/content/public/browser/browser_message_filter.h
@@ -24,6 +24,7 @@ class MessageFilter;
 }
 
 namespace content {
+class BrowserMessageFilterPeer;
 struct BrowserMessageFilterTraits;
 
 // Base class for message filters in the browser process.  You can receive and
@@ -39,10 +40,10 @@ class CONTENT_EXPORT BrowserMessageFilter
 
   // These match the corresponding IPC::MessageFilter methods and are always
   // called on the IO thread.
-  virtual void OnFilterAdded(IPC::Channel* channel) {}
+  virtual void OnFilterAdded(IPC::Sender* sender) {}
   virtual void OnFilterRemoved() {}
-  virtual void OnChannelClosing() {}
-  virtual void OnChannelConnected(int32 peer_pid) {}
+  virtual void OnSenderClosing() {}
+  virtual void OnSenderConnected() {}
 
   // Called when the message filter is about to be deleted.  This gives
   // derived classes the option of controlling which thread they're deleted
@@ -77,15 +78,15 @@ class CONTENT_EXPORT BrowserMessageFilter
   // your function will be called on the requested thread.
   virtual bool OnMessageReceived(const IPC::Message& message) = 0;
 
-  // Can be called on any thread, after OnChannelConnected is called.
+  // Can be called on any thread, after OnSenderConnected is called.
   base::ProcessHandle PeerHandle();
 
-  // Can be called on any thread, after OnChannelConnected is called.
-  base::ProcessId peer_pid() const { return peer_pid_; }
+  // Can be called on any thread, after OnSenderConnected is called.
+  base::ProcessId peer_pid() const;
 
-  void set_peer_pid_for_testing(base::ProcessId peer_pid) {
-    peer_pid_ = peer_pid;
-  }
+  // Tells the peer process of the host.
+  void OnFilterAddedToHost(BrowserMessageFilterPeer* peer);
+  void OnFilterRemovedFromHost();
 
   // Checks that the given message can be dispatched on the UI thread, depending
   // on the platform.  If not, returns false and an error ot the sender.
@@ -123,15 +124,10 @@ class CONTENT_EXPORT BrowserMessageFilter
   // child class does in its OnDestruct method.
   Internal* internal_;
 
-  IPC::Channel* channel_;
-  base::ProcessId peer_pid_;
+  IPC::Sender* sender_;
+  BrowserMessageFilterPeer* peer_;
 
   std::vector<uint32> message_classes_to_filter_;
-
-#if defined(OS_WIN)
-  base::Lock peer_handle_lock_;
-  base::ProcessHandle peer_handle_;
-#endif
 };
 
 struct BrowserMessageFilterTraits {