Don't share same name for js proxies cache.

sdk/lib/_internal/compiler/implementation/js_emitter/code_emitter_task.dart

Index: sdk/lib/_internal/compiler/implementation/js_emitter/code_emitter_task.dart
diff --git a/sdk/lib/_internal/compiler/implementation/js_emitter/code_emitter_task.dart b/sdk/lib/_internal/compiler/implementation/js_emitter/code_emitter_task.dart
index 6b79cb780c543fec2e95fdec7f0ad98d89755fad..5e5ff6495b4c15b9f53c4050cadc37be85c2fed1 100644
--- a/sdk/lib/_internal/compiler/implementation/js_emitter/code_emitter_task.dart
+++ b/sdk/lib/_internal/compiler/implementation/js_emitter/code_emitter_task.dart
@@ -975,14 +975,6 @@ class CodeEmitterTask extends CompilerTask {
   jsAst.Expression generateDispatchPropertyInitialization() {
     return js('!#', js.fun([], [
 
-        // On V8, the 'intern' function converts a string to a symbol, which
-        // makes property access much faster.
-        new jsAst.FunctionDeclaration(new jsAst.VariableDeclaration('intern'),
-            js.fun(['s'], [
-                js('var o = {}'),
-                js('o[s] = 1'),
-                js.return_(js('Object.keys(convertToFastObject(o))[0]'))])),
-
         // To ensure that different programs loaded into the same context (page)
         // use distinct dispatch properies, we place an object on `Object` to
         // contain the names already in use.
@@ -992,7 +984,7 @@ class CodeEmitterTask extends CompilerTask {
 
         js('var rootProperty = "${generateDispatchPropertyName()}"'),
         js.for_('var i = 0', null, 'i++', [
-            js('property = intern(rootProperty + "_" + i + "_")'),
+            js('property = convertToJSSymbol(rootProperty + "_" + i + "_")'),
             js.if_('!(property in usedProperties)', [
                 js('usedProperties[property] = 1'),
                 js.return_(
@@ -1164,7 +1156,8 @@ class CodeEmitterTask extends CompilerTask {
   void emitConvertToFastObjectFunction() {
     // Create an instance that uses 'properties' as prototype. This should make
     // 'properties' a fast object.
-    mainBuffer.add(r'''function convertToFastObject(properties) {
+    mainBuffer.add(r'''
+function convertToFastObject(properties) {
   function MyClass() {};
   MyClass.prototype = properties;
   new MyClass();
@@ -1185,10 +1178,19 @@ if (typeof $printHelperName === "function") {
 }
 ''');
     }
-mainBuffer.add(r'''
+    mainBuffer.add(r'''
   return properties;
 }
 ''');
+    // On V8, the 'intern' function converts a string to a symbol, which
+    // makes property access much faster.
+    mainBuffer.add(r'''
+function convertToJSSymbol(s) {
+  var o = {};
+  o[s] = 1;
+  return Object.keys(convertToFastObject(o))[0];
+}
+''');
   }
 
   void writeLibraryDescriptors(LibraryElement library) {