Add an end-to-end test that excercises Mojo with a sandbox.

content/common/mojo_test.mojom

Index: content/common/mojo_test.mojom
diff --git a/tools/clang/rewrite_to_chrome_style/tests/gen/thing.h b/content/common/mojo_test.mojom
similarity index 61%
copy from tools/clang/rewrite_to_chrome_style/tests/gen/thing.h
copy to content/common/mojo_test.mojom
index 900b65c4cc4d0a285729491e4d03ed6f3a52b0f3..57a652864cb2131763cc1ed9b8b0bdbac4ef3240 100644
--- a/tools/clang/rewrite_to_chrome_style/tests/gen/thing.h
+++ b/content/common/mojo_test.mojom
@@ -2,10 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-namespace blink {
-void genThing();
+module content.mojom;
 
-class GenClass {
-  virtual void genMethod() {}
+interface MojoTest {
+  MakeSharedBuffer(uint32 size) => (handle<shared_buffer> ?shm);
 };
-}