Mojo JS bindings: add support to generate "dual-mode" code.

mojo/public/tools/bindings/pylib/mojom/generate/generator.py

Index: mojo/public/tools/bindings/pylib/mojom/generate/generator.py
diff --git a/mojo/public/tools/bindings/pylib/mojom/generate/generator.py b/mojo/public/tools/bindings/pylib/mojom/generate/generator.py
index 2778dcb25825f850c03fe94976725eee8e85e0ff..56546c2b957d3fffb29f6b9cd444f8cb4868be02 100644
--- a/mojo/public/tools/bindings/pylib/mojom/generate/generator.py
+++ b/mojo/public/tools/bindings/pylib/mojom/generate/generator.py
@@ -155,7 +155,7 @@ class Generator(object):
   # files to stdout.
   def __init__(self, module, output_dir=None, typemap=None, variant=None,
                bytecode_path=None, for_blink=False, use_once_callback=False,
-               use_new_js_bindings=False, export_attribute=None,
+               js_bindings_mode="new", export_attribute=None,
                export_header=None, generate_non_variant_code=False):
     self.module = module
     self.output_dir = output_dir
@@ -164,7 +164,7 @@ class Generator(object):
     self.bytecode_path = bytecode_path
     self.for_blink = for_blink
     self.use_once_callback = use_once_callback
-    self.use_new_js_bindings = use_new_js_bindings
+    self.js_bindings_mode = js_bindings_mode
     self.export_attribute = export_attribute
     self.export_header = export_header
     self.generate_non_variant_code = generate_non_variant_code