Revert of [mojo-edk] Simplify multiprocess pipe bootstrap

mojo/edk/system/core.h

Index: mojo/edk/system/core.h
diff --git a/mojo/edk/system/core.h b/mojo/edk/system/core.h
index 603cba9082c8e8ed6d7af494f5b7d0e256da2481..8e9af8eddb5dfaf691d59dad3a24df1cb34c5bfa 100644
--- a/mojo/edk/system/core.h
+++ b/mojo/edk/system/core.h
@@ -52,19 +52,26 @@
   // Called in a child process exactly once during early initialization.
   void InitChild(ScopedPlatformHandle platform_handle);
 
-  // Creates a message pipe endpoint connected to an endpoint in a remote
+  // This creates a message pipe endpoint connected to an endpoint in a remote
   // embedder. |platform_handle| is used as a channel to negotiate the
-  // connection.
-  ScopedMessagePipeHandle CreateMessagePipe(
-      ScopedPlatformHandle platform_handle);
+  // connection. This is only here to facilitate legacy embedder code. See
+  // mojo::edk::CreateMessagePipe in mojo/edk/embedder/embedder.h.
+  void CreateMessagePipe(
+      ScopedPlatformHandle platform_handle,
+      const base::Callback<void(ScopedMessagePipeHandle)>& callback);
 
   // Creates a message pipe endpoint associated with |token|, which a child
   // holding the token can later locate and connect to.
-  ScopedMessagePipeHandle CreateParentMessagePipe(const std::string& token);
-
-  // Creates a message pipe endpoint and connects it to a pipe the parent has
-  // associated with |token|.
-  ScopedMessagePipeHandle CreateChildMessagePipe(const std::string& token);
+  void CreateParentMessagePipe(
+      const std::string& token,
+      const base::Callback<void(ScopedMessagePipeHandle)>& callback);
+
+  // Creates a message pipe endpoint associated with |token|, which will be
+  // passed to the parent in order to find an associated remote port and connect
+  // to it.
+  void CreateChildMessagePipe(
+      const std::string& token,
+      const base::Callback<void(ScopedMessagePipeHandle)>& callback);
 
   MojoHandle AddDispatcher(scoped_refptr<Dispatcher> dispatcher);