Mojo JS bindings: flip the default value of use_new_js_bindings to true.

mojo/public/interfaces/bindings/BUILD.gn

 # Copyright 2015 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("../../tools/bindings/mojom.gni")
 
 mojom("bindings") {
   visibility = []
   sources = [
     "interface_control_messages.mojom",
     "pipe_control_messages.mojom",
   ]
 
   component_output_prefix = "mojo_public_interfaces_bindings"
   export_class_attribute = "MOJO_CPP_BINDINGS_EXPORT"
   export_define = "MOJO_CPP_BINDINGS_IMPLEMENTATION"
   export_header = "mojo/public/cpp/bindings/bindings_export.h"
 
   export_class_attribute_shared = "MOJO_CPP_BINDINGS_EXPORT"
   export_define_shared = "MOJO_CPP_BINDINGS_IMPLEMENTATION"
   export_header_shared = "mojo/public/cpp/bindings/bindings_export.h"
+
+  use_new_js_bindings = false
 }
 
 # TODO(yzshen): Remove this target and use the one above once
 # |use_new_js_bindings| becomes true by default.
 mojom("new_bindings") {
   visibility = []
   sources = [
     "new_bindings/interface_control_messages.mojom",
     "new_bindings/pipe_control_messages.mojom",
   ]
-
-  use_new_js_bindings = true
 }