Serve mojo WebUI resources from the same origin as the WebUI itself.

content/renderer/mojo_context_state.h

Index: content/renderer/mojo_context_state.h
diff --git a/content/renderer/mojo_context_state.h b/content/renderer/mojo_context_state.h
index 96110420f931067c6fbec9378e99c063af1c87c5..f6516b4f71a452b3469338cff28400ce88042f6a 100644
--- a/content/renderer/mojo_context_state.h
+++ b/content/renderer/mojo_context_state.h
@@ -76,6 +76,9 @@ class MojoContextState : public gin::ModuleRegistryObserver {
   // Set of modules we've fetched script from.
   std::set<std::string> fetched_modules_;
 
+  // The prefix to use for all module requests.
+  const std::string module_prefix_;
+
   DISALLOW_COPY_AND_ASSIGN(MojoContextState);
 };