dart2js: Store mapTypeToInterceptor in embedded global.

sdk/lib/_internal/compiler/js_lib/interceptors.dart

 // Copyright (c) 2012, 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 _interceptors;
 
 import 'dart:_js_embedded_names' show
-    DISPATCH_PROPERTY_NAME;
+    DISPATCH_PROPERTY_NAME,
+    MAP_TYPE_TO_INTERCEPTOR;
 
 import 'dart:collection';
 import 'dart:_internal' hide Symbol;
 import "dart:_internal" as _symbol_dev show Symbol;
 import 'dart:_js_helper' show allMatchesInStringUnchecked,
                               Null,
                               JSSyntaxRegExp,
                               Primitives,
                               checkInt,
                               checkNull,
@@ skipping 170 matching lines @@
  * JavaScript object map for the constructors.
  *
  * The value of this variable is set by the compiler and contains only types
  * that are user extensions of native classes where the type occurs as a
  * constant in the program.
  *
  * The compiler, in CustomElementsAnalysis, assumes that [mapTypeToInterceptor]
  * is accessed only by code that also calls [findIndexForWebComponentType].  If
  * this assumption is invalidated, the compiler will have to be updated.
  */
-// TODO(sra): Mark this as initialized to a constant with unknown value.
-var mapTypeToInterceptor;
+get mapTypeToInterceptor {
+  return JS_EMBEDDED_GLOBAL('', MAP_TYPE_TO_INTERCEPTOR);
+}
 
 int findIndexForNativeSubclassType(Type type) {
   if (JS('bool', '# == null', mapTypeToInterceptor)) return null;
   List map = JS('JSFixedArray', '#', mapTypeToInterceptor);
   for (int i = 0; i + 1 < map.length; i += 3) {
     if (type == map[i]) {
       return i;
     }
   }
   return null;
@@ skipping 192 matching lines @@
  * Interceptor for unclassified JavaScript objects, typically objects with a
  * non-trivial prototype chain.
  *
  * This class also serves as a fallback for unknown JavaScript exceptions.
  */
 class UnknownJavaScriptObject extends JavaScriptObject {
   const UnknownJavaScriptObject();
 
   String toString() => JS('String', 'String(#)', this);
 }