Remove usage of dart:json.

tools/dom/templates/html/dartium/html_dartium.darttemplate

Index: tools/dom/templates/html/dartium/html_dartium.darttemplate
diff --git a/tools/dom/templates/html/dartium/html_dartium.darttemplate b/tools/dom/templates/html/dartium/html_dartium.darttemplate
index dded4de0b918feb0925af5d3a162b89c1dd98bc4..aa6dd64d036616cf82cc3eb3b33f504e23081ff1 100644
--- a/tools/dom/templates/html/dartium/html_dartium.darttemplate
+++ b/tools/dom/templates/html/dartium/html_dartium.darttemplate
@@ -18,7 +18,7 @@ import 'dart:_collection-dev' hide Symbol, deprecated;
 import 'dart:html_common';
 import 'dart:indexed_db';
 import 'dart:isolate';
-import 'dart:json' as json;
+import "dart:convert";
 import 'dart:math';
 // TODO(vsm): Remove this when we can do the proper checking in
 // native code for custom elements.
@@ -110,7 +110,7 @@ var _callPortLastResult = null;
 _callPortSync(num id, var message) {
   if (!_callPortInitialized) {
     window.on['js-result'].listen((event) {
-      _callPortLastResult = json.parse(_getPortSyncEventData(event));
+      _callPortLastResult = JSON.decode(_getPortSyncEventData(event));
     });
     _callPortInitialized = true;
   }