[mojo] Add typemap and variant support to generators

mojo/public/tools/bindings/generators/mojom_js_generator.py

Index: mojo/public/tools/bindings/generators/mojom_js_generator.py
diff --git a/mojo/public/tools/bindings/generators/mojom_js_generator.py b/mojo/public/tools/bindings/generators/mojom_js_generator.py
index 23c203a52e0231d003987f1b4efd201cd503c74a..638f1cb0a0134d9b9fba134b98c9d309d53ea68c 100644
--- a/mojo/public/tools/bindings/generators/mojom_js_generator.py
+++ b/mojo/public/tools/bindings/generators/mojom_js_generator.py
@@ -385,6 +385,9 @@ class Generator(generator.Generator):
     return self.GetParameters()
 
   def GenerateFiles(self, args):
+    if self.variant:
+      raise Exception("Variants not supported in JavaScript bindings.")
+
     self.Write(self.GenerateAMDModule(),
         self.MatchMojomFilePath("%s.js" % self.module.name))