Check for duplicate library names

lib/runtime/dart/_interceptors.js

-var _interceptors = dart.defineLibrary(_interceptors, {});
-var core = dart.import(core);
-var _js_helper = dart.lazyImport(_js_helper);
-var _internal = dart.import(_internal);
-var _foreign_helper = dart.import(_foreign_helper);
-var _js_embedded_names = dart.import(_js_embedded_names);
+dart.defineLibrary('_interceptors');
+dart.import('core');
+dart.lazyImport('_js_helper');
+dart.import('_internal');
+dart.import('_foreign_helper');
+dart.import('_js_embedded_names');
 (function(exports, core, _js_helper, _internal, _foreign_helper, _js_embedded_names) {
   'use strict';
   let JSArray = Array;
   let JSMutableArray$ = dart.generic(function(E) {
     class JSMutableArray extends JSArray$(E) {
       JSMutableArray() {
         super.JSArray();
       }
     }
     JSMutableArray[dart.implements] = () => [JSMutableIndexable];
@@ skipping 1196 matching lines @@
   exports.findInterceptorForType = findInterceptorForType;
   exports.JSBool = JSBool;
   exports.JSNull = JSNull;
   exports.JSIndexable = JSIndexable;
   exports.JSMutableIndexable = JSMutableIndexable;
   exports.JSObject = JSObject;
   exports.JavaScriptObject = JavaScriptObject;
   exports.PlainJavaScriptObject = PlainJavaScriptObject;
   exports.UnknownJavaScriptObject = UnknownJavaScriptObject;
 })(_interceptors, core, _js_helper, _internal, _foreign_helper, _js_embedded_names);