Remove IPC::Endpoint.

BUG=659448
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel

Review-Url: https://codereview.chromium.org/2493623002
Cr-Commit-Position: refs/heads/master@{#431381}
diff --git a/ipc/ipc_message_pipe_reader.h b/ipc/ipc_message_pipe_reader.h
index cd881498..65e01ae 100644
--- a/ipc/ipc_message_pipe_reader.h
+++ b/ipc/ipc_message_pipe_reader.h
@@ -48,7 +48,7 @@
  public:
   class Delegate {
    public:
-    virtual void OnPeerPidReceived() = 0;
+    virtual void OnPeerPidReceived(int32_t peer_pid) = 0;
     virtual void OnMessageReceived(const Message& message) = 0;
     virtual void OnPipeError() = 0;
     virtual void OnAssociatedInterfaceRequest(
@@ -86,8 +86,6 @@
   void GetRemoteInterface(const std::string& name,
                           mojo::ScopedInterfaceEndpointHandle handle);
 
-  base::ProcessId GetPeerPid() const { return peer_pid_; }
-
   mojom::Channel* sender() const { return sender_.get(); }
 
  protected:
@@ -106,7 +104,6 @@
 
   // |delegate_| is null once the message pipe is closed.
   Delegate* delegate_;
-  base::ProcessId peer_pid_ = base::kNullProcessId;
   mojom::ChannelAssociatedPtr sender_;
   mojo::AssociatedBinding<mojom::Channel> binding_;
   base::ThreadChecker thread_checker_;