[mojo] Use a pipe path to initialise Mojo in elevated utility processes.

mojo/edk/embedder/platform_handle.h

Index: mojo/edk/embedder/platform_handle.h
diff --git a/mojo/edk/embedder/platform_handle.h b/mojo/edk/embedder/platform_handle.h
index 675dd1fe9c8f480c1a5e4fd42120dfc6007d16f5..60c6adcc3d62c8c7841cce19a82a5bbfb611c965 100644
--- a/mojo/edk/embedder/platform_handle.h
+++ b/mojo/edk/embedder/platform_handle.h
@@ -72,6 +72,10 @@ struct MOJO_SYSTEM_IMPL_EXPORT PlatformHandle {
   // A Windows HANDLE may be duplicated to another process but not yet sent to
   // that process. This tracks the handle's owning process.
   base::ProcessHandle owning_process;
+
+  // A Windows HANDLE may be an unconnected named pipe. In this case, we need to
+  // wait for a connection before communicating on the pipe.
+  bool needs_connection = false;
 };
 #else
 #error "Platform not yet supported."