mus: Make --use-mus-in-renderer work again.

content/browser/renderer_host/render_process_host_impl.cc

Index: content/browser/renderer_host/render_process_host_impl.cc
diff --git a/content/browser/renderer_host/render_process_host_impl.cc b/content/browser/renderer_host/render_process_host_impl.cc
index 191eb9adf22bac54003096297857f0532fbfa203..7c15800a870e42a3e0060081e38b56fc5079d2d5 100644
--- a/content/browser/renderer_host/render_process_host_impl.cc
+++ b/content/browser/renderer_host/render_process_host_impl.cc
@@ -1560,6 +1560,9 @@ void RenderProcessHostImpl::PropagateBrowserCommandLineToRenderer(
 #if defined(OS_CHROMEOS)
     switches::kDisableVaapiAcceleratedVideoEncode,
 #endif
+#if defined(MOJO_SHELL_CLIENT)
+    switches::kUseMusInRenderer,
+#endif
   };
   renderer_cmd->CopySwitchesFrom(browser_cmd, kSwitchNames,
                                  arraysize(kSwitchNames));