ipc: Make a common subclass for Channel and ProxyChannel.

ipc/ipc_channel_proxy.h

Index: ipc/ipc_channel_proxy.h
diff --git a/ipc/ipc_channel_proxy.h b/ipc/ipc_channel_proxy.h
index b01ccbc237408fe23cec60e06ee32ea46a28f07b..714bafddf89a471d76e421a0edfff797fbe8a6fe 100644
--- a/ipc/ipc_channel_proxy.h
+++ b/ipc/ipc_channel_proxy.h
@@ -13,6 +13,7 @@
 #include "base/threading/non_thread_safe.h"
 #include "ipc/ipc_channel.h"
 #include "ipc/ipc_channel_handle.h"
+#include "ipc/ipc_endpoint.h"
 #include "ipc/ipc_listener.h"
 #include "ipc/ipc_sender.h"
 
@@ -63,7 +64,7 @@ class SendCallbackHelper;
 // |channel_lifetime_lock_| is used to protect it. The locking overhead is only
 // paid if the underlying channel supports thread-safe |Send|.
 //
-class IPC_EXPORT ChannelProxy : public Sender, public base::NonThreadSafe {
+class IPC_EXPORT ChannelProxy : public Endpoint, public base::NonThreadSafe {
  public:
 #if defined(ENABLE_IPC_FUZZER)
   // Interface for a filter to be imposed on outgoing messages which can
@@ -147,9 +148,9 @@ class IPC_EXPORT ChannelProxy : public Sender, public base::NonThreadSafe {
   // Called to clear the pointer to the IPC task runner when it's going away.
   void ClearIPCTaskRunner();
 
-  // Get the process ID for the connected peer.
-  // Returns base::kNullProcessId if the peer is not connected yet.
-  base::ProcessId GetPeerPID() const { return context_->peer_pid_; }
+  // Endpoint overrides.
+  base::ProcessId GetPeerPID() const override;
+  void OnSetAttachmentBrokerEndpoint() override;
 
 #if defined(OS_POSIX) && !defined(OS_NACL_SFI)
   // Calls through to the underlying channel's methods.
@@ -157,8 +158,6 @@ class IPC_EXPORT ChannelProxy : public Sender, public base::NonThreadSafe {
   base::ScopedFD TakeClientFileDescriptor();
 #endif
 
-  void SetAttachmentBrokerEndpoint(bool is_endpoint);
-
  protected:
   class Context;
   // A subclass uses this constructor if it needs to add more information