Polyfill only once

pkg/dev_compiler/tool/input_sdk/private/ddc_runtime/runtime.dart

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library dart._runtime;
 
 import 'dart:async';
 import 'dart:collection';
 
 import 'dart:_debugger' show stackTraceMapper;
@@ skipping 18 matching lines @@
 part 'types.dart';
 part 'errors.dart';
 part 'generators.dart';
 part 'operations.dart';
 part 'profile.dart';
 part 'utils.dart';
 
 // TODO(vsm): Move polyfill code to dart:html.
 // Note, native extensions are registered onto types in dart.global.
 // This polyfill needs to run before the corresponding dart:html code is run.
-final polyfill = JS(
+final _polyfilled = JS('', 'Symbol("_polyfilled")');
+
+bool polyfill(window) => JS(
     '',
-    '''
-function (window) {
-  if (typeof window.NodeList !== "undefined") {
+    '''(() => {
+  if ($window[$_polyfilled]) return false;
+  $window[$_polyfilled] = true;  
+
+  if (typeof $window.NodeList !== "undefined") {
     // TODO(vsm): Do we still need these?
-    window.NodeList.prototype.get = function(i) { return this[i]; };
-    window.NamedNodeMap.prototype.get = function(i) { return this[i]; };
-    window.DOMTokenList.prototype.get = function(i) { return this[i]; };
-    window.HTMLCollection.prototype.get = function(i) { return this[i]; };
+    $window.NodeList.prototype.get = function(i) { return this[i]; };
+    $window.NamedNodeMap.prototype.get = function(i) { return this[i]; };
+    $window.DOMTokenList.prototype.get = function(i) { return this[i]; };
+    $window.HTMLCollection.prototype.get = function(i) { return this[i]; };
 
     // Expose constructors for DOM types dart:html needs to assume are
     // available on window.
-    if (typeof window.PannerNode == "undefined") {
+    if (typeof $window.PannerNode == "undefined") {
       let audioContext;
-      if (typeof window.AudioContext == "undefined" &&
-          (typeof window.webkitAudioContext != "undefined")) {
-        audioContext = new window.webkitAudioContext();
+      if (typeof $window.AudioContext == "undefined" &&
+          (typeof $window.webkitAudioContext != "undefined")) {
+        audioContext = new $window.webkitAudioContext();
       } else {
-        audioContext = new window.AudioContext();
-        window.StereoPannerNode =
+        audioContext = new $window.AudioContext();
+        $window.StereoPannerNode =
             audioContext.createStereoPanner().constructor;
       }
-      window.PannerNode = audioContext.createPanner().constructor;
+      $window.PannerNode = audioContext.createPanner().constructor;
     }
-    if (typeof window.AudioSourceNode == "undefined") {
-      window.AudioSourceNode = MediaElementAudioSourceNode.__proto__;
+    if (typeof $window.AudioSourceNode == "undefined") {
+      $window.AudioSourceNode = MediaElementAudioSourceNode.__proto__;
     }
-    if (typeof window.FontFaceSet == "undefined") {
+    if (typeof $window.FontFaceSet == "undefined") {
       // CSS Font Loading is not supported on Edge.
-      if (typeof window.document.fonts != "undefined") {
-        window.FontFaceSet = window.document.fonts.__proto__.constructor;
+      if (typeof $window.document.fonts != "undefined") {
+        $window.FontFaceSet = $window.document.fonts.__proto__.constructor;
       }
     }
-    if (typeof window.MemoryInfo == "undefined") {
-      if (typeof window.performance.memory != "undefined") {
-        window.MemoryInfo = window.performance.memory.constructor;
+    if (typeof $window.MemoryInfo == "undefined") {
+      if (typeof $window.performance.memory != "undefined") {
+        $window.MemoryInfo = $window.performance.memory.constructor;
       }
     }
-    if (typeof window.Geolocation == "undefined") {
-      window.Geolocation == window.navigator.geolocation.constructor;
+    if (typeof $window.Geolocation == "undefined") {
+      $window.Geolocation == $window.navigator.geolocation.constructor;
     }
-    if (typeof window.Animation == "undefined") {
-      let d = window.document.createElement('div');
+    if (typeof $window.Animation == "undefined") {
+      let d = $window.document.createElement('div');
       if (typeof d.animate != "undefined") {
-        window.Animation = d.animate(d).constructor;
+        $window.Animation = d.animate(d).constructor;
       }
     }
-    if (typeof window.SourceBufferList == "undefined") {
-      window.SourceBufferList =
-        new window.MediaSource().sourceBuffers.constructor;
+    if (typeof $window.SourceBufferList == "undefined") {
+      $window.SourceBufferList =
+        new $window.MediaSource().sourceBuffers.constructor;
     }
-    if (typeof window.SpeechRecognition == "undefined") {
-      window.SpeechRecognition = window.webkitSpeechRecognition;
-      window.SpeechRecognitionError = window.webkitSpeechRecognitionError;
-      window.SpeechRecognitionEvent = window.webkitSpeechRecognitionEvent;
+    if (typeof $window.SpeechRecognition == "undefined") {
+      $window.SpeechRecognition = $window.webkitSpeechRecognition;
+      $window.SpeechRecognitionError = $window.webkitSpeechRecognitionError;
+      $window.SpeechRecognitionEvent = $window.webkitSpeechRecognitionEvent;
     }
   }
-}
-''');
+  return true;
+})()''');
 
 @JSExportName('global')
 final global_ = JS(
     '',
     '''
   function () {
     // Find global object.
     var globalState = (typeof window != "undefined") ? window
       : (typeof global != "undefined") ? global
       : (typeof self != "undefined") ? self : {};
@@ skipping 16 matching lines @@
         'failForWeakModeIsChecks' in settings ?
             settings.failForWeakModeIsChecks : true);
     $trackProfile(
         'trackProfile' in settings ? settings.trackProfile : false);
 
     return globalState;
   }()
 ''');
 
 final JsSymbol = JS('', 'Symbol');