Mojo message validation tests: add integration tests and move existing conformance tests.

mojo/apps/js/test/js_to_cpp_unittest.cc

Index: mojo/apps/js/test/js_to_cpp_unittest.cc
diff --git a/mojo/apps/js/test/js_to_cpp_unittest.cc b/mojo/apps/js/test/js_to_cpp_unittest.cc
index 74bc7ed6ec0c790b808b8201ad666b5ef1cc4081..6077ddf1d92ebccd5593e2d7127a9f89d99a6968 100644
--- a/mojo/apps/js/test/js_to_cpp_unittest.cc
+++ b/mojo/apps/js/test/js_to_cpp_unittest.cc
@@ -394,8 +394,7 @@ class JsToCppTest : public testing::Test {
         MakeProxy<js_to_cpp::JsSide>(pipe.handle0.Pass());
     js_side.set_client(cpp_side);
 
-    js_side.internal_state()->router()->
-        set_enforce_errors_from_incoming_receiver(false);
+    js_side.internal_state()->router()->EnableTestingMode();
 
     cpp_side->set_js_side(js_side.get());