IPC: Fix attachment brokering race condition.

ipc/ipc_channel.h

Index: ipc/ipc_channel.h
diff --git a/ipc/ipc_channel.h b/ipc/ipc_channel.h
index c1ad4172bd169f590d025314c027e8e7ef853c4e..6653939f153193a95994680a6c4971e8e727bfb9 100644
--- a/ipc/ipc_channel.h
+++ b/ipc/ipc_channel.h
@@ -165,6 +165,8 @@ class IPC_EXPORT Channel : public Endpoint {
   // connect to a pre-existing pipe.  Note, calling Connect()
   // will not block the calling thread and may complete
   // asynchronously.
+  //
+  // The subclass implementation must call OnConnect().

[Tom Sepez, 2016/04/22 00:33:22]

nit: when? "when the connection is completed"? or what happens?

[erikchen, 2016/04/22 01:42:18]

I renamed the method to WillConnect() and updated the comment to indicate that
the method must be called at the beginning of the implementation.

This exists entirely to power the DCHECK in OnSetAttachmentBrokerEndpoint() to
prevent this error from happening again.

   virtual bool Connect() WARN_UNUSED_RESULT = 0;
 
   // Close this Channel explicitly.  May be called multiple times.
@@ -255,6 +257,15 @@ class IPC_EXPORT Channel : public Endpoint {
     void* buffer_;
     size_t length_;
   };
+
+  // Endpoint overrides.
+  void OnSetAttachmentBrokerEndpoint() override;
+
+  // Subclasses should call this method after connecting.

[Tom Sepez, 2016/04/22 00:33:22]

should vs. must?

[erikchen, 2016/04/22 01:42:18]

Updated the comment to use MUST.

+  void OnConnect();
+
+ private:
+  bool did_connect_ = false;
 };
 
 #if defined(OS_POSIX)