Revert of [mojo-edk] Simplify multiprocess pipe bootstrap

mojo/shell/runner/child/runner_connection.cc

Index: mojo/shell/runner/child/runner_connection.cc
diff --git a/mojo/shell/runner/child/runner_connection.cc b/mojo/shell/runner/child/runner_connection.cc
index 313c00a338d7bdade01b3a465639378835f78a0b..75b4648dc0db58f70f7753fe65959533d4e84baa 100644
--- a/mojo/shell/runner/child/runner_connection.cc
+++ b/mojo/shell/runner/child/runner_connection.cc
@@ -74,6 +74,13 @@
 using GotApplicationRequestCallback =
     base::Callback<void(InterfaceRequest<mojom::ShellClient>)>;
 
+void OnCreateMessagePipe(ScopedMessagePipeHandle* result,
+                         Blocker::Unblocker unblocker,
+                         ScopedMessagePipeHandle pipe) {
+  *result = std::move(pipe);
+  unblocker.Unblock(base::Bind(&base::DoNothing));
+}
+
 void OnGotApplicationRequest(InterfaceRequest<mojom::ShellClient>* out_request,
                              InterfaceRequest<mojom::ShellClient> request) {
   *out_request = std::move(request);
@@ -222,10 +229,13 @@
     std::string primordial_pipe_token =
         base::CommandLine::ForCurrentProcess()->GetSwitchValueASCII(
             switches::kPrimordialPipeToken);
-    handle = edk::CreateChildMessagePipe(primordial_pipe_token);
-  }
-
-  DCHECK(handle.is_valid());
+    Blocker blocker;
+    edk::CreateChildMessagePipe(
+        primordial_pipe_token,
+        base::Bind(&OnCreateMessagePipe, base::Unretained(&handle),
+                   blocker.GetUnblocker()));
+    blocker.Block();
+  }
 
   Blocker blocker;
   controller_runner_->PostTask(