Adds plumbing to pass WebUI mojo::Handle from browser to renderer

mojo/mojo_services.gypi

Index: mojo/mojo_services.gypi
diff --git a/mojo/mojo_services.gypi b/mojo/mojo_services.gypi
index e3c8bb5b4e308f40075e21ca785a3cd7e5e01974..10134060b75f1f72ac68ec86728d5d5ab9bb9625 100644
--- a/mojo/mojo_services.gypi
+++ b/mojo/mojo_services.gypi
@@ -8,6 +8,9 @@
         'services/gles2/command_buffer_type_conversions.cc',
         'services/gles2/command_buffer_type_conversions.h',
       ],
+      'variables': {
+        'mojom_base_output_dir': 'mojo',
+      },
       'includes': [ 'public/bindings/mojom_bindings_generator.gypi' ],
       'export_dependent_settings': [
         'mojo_bindings',
@@ -43,6 +46,9 @@
       'sources': [
         'services/native_viewport/native_viewport.mojom',
       ],
+      'variables': {
+        'mojom_base_output_dir': 'mojo',
+      },
       'includes': [ 'public/bindings/mojom_bindings_generator.gypi' ],
       'export_dependent_settings': [
         'mojo_bindings',