Move existing Mojo JS <--> CPP tests out of webui test harness.

mojo/mojo_apps.gypi

Index: mojo/mojo_apps.gypi
diff --git a/mojo/mojo_apps.gypi b/mojo/mojo_apps.gypi
index fe8d65edecaf327dbe7a8689690233e6a05c3151..364e0aa8ab86b0a3b734534acaaf330d3a51e375 100644
--- a/mojo/mojo_apps.gypi
+++ b/mojo/mojo_apps.gypi
@@ -37,10 +37,28 @@
       ],
     },
     {
+      'target_name': 'mojo_apps_js_bindings',
+      'type': 'static_library',
+      'sources': [
+        'apps/js/test/js_to_cpp.mojom',
+      ],
+      'variables': {
+        'mojom_base_output_dir': 'mojo',
+      },
+      'includes': [ 'public/tools/bindings/mojom_bindings_generator.gypi' ],
+      'export_dependent_settings': [
+        'mojo_cpp_bindings',
+      ],
+      'dependencies': [
+        'mojo_cpp_bindings',
+      ],
+    },
+    {
       'target_name': 'mojo_apps_js_unittests',
       'type': 'executable',
       'dependencies': [
         '../gin/gin.gyp:gin_test',
+        'mojo_apps_js_bindings',
         'mojo_common_lib',
         'mojo_common_test_support',
         'mojo_js_lib',