Embed a mojo ApplicationManager in content/browser

content/public/test/test_mojo_service.mojom

Index: content/public/test/test_mojo_service.mojom
diff --git a/tools/clang/blink_gc_plugin/tests/traceimpl_omitted_trace.cpp b/content/public/test/test_mojo_service.mojom
similarity index 70%
copy from tools/clang/blink_gc_plugin/tests/traceimpl_omitted_trace.cpp
copy to content/public/test/test_mojo_service.mojom
index b6dc2dffe589999c1be755a4ecef4f7dfd55e6ff..e4179168ff3f60949b153b971764fe0337b3d31e 100644
--- a/tools/clang/blink_gc_plugin/tests/traceimpl_omitted_trace.cpp
+++ b/content/public/test/test_mojo_service.mojom
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#include "traceimpl_omitted_trace.h"
+module content;
 
-// Nothing to define here.
+interface TestMojoService {
+  DoSomething() => ();
+};