Do not use full substitution when only computing single type variables.

pkg/compiler/lib/src/js_emitter/old_emitter/emitter.dart

 // Copyright (c) 2014, 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.
 
 part of dart2js.js_emitter;
 
 
 class OldEmitter implements Emitter {
   final Compiler compiler;
   final CodeEmitterTask task;
@@ skipping 914 matching lines @@
                                    }''',
                          [namer.isolateName, makeConstListProperty]),
             compiler, monitor: compiler.dumpInfoTask));
     output.add(N);
   }
 
   void emitFunctionThatReturnsNull(CodeOutput output) {
     output.addBuffer(
         jsAst.prettyPrint(
             js.statement('#.# = function() {}',
-                         [backend.namer.isolateName,
+                         [backend.namer.currentIsolate,
                           backend.rti.getFunctionThatReturnsNullName]),
             compiler, monitor: compiler.dumpInfoTask));
     output.add(N);
   }
 
   jsAst.Expression generateFunctionThatReturnsNull() {
-    return js("#.#", [backend.namer.isolateName,
+    return js("#.#", [backend.namer.currentIsolate,
                       backend.rti.getFunctionThatReturnsNullName]);
   }
 
   /// Returns the code equivalent to:
   ///   `function(args) { $.startRootIsolate(X.main$closure(), args); }`
   jsAst.Expression buildIsolateSetupClosure(Element appMain,
                                             Element isolateMain) {
     jsAst.Expression mainAccess = isolateStaticClosureAccess(appMain);
     // Since we pass the closurized version of the main method to
     // the isolate method, we must make sure that it exists.
@@ skipping 1142 matching lines @@
     for (Element element in compiler.enqueuer.codegen.newlyEnqueuedElements) {
       if (element.isInstanceMember) {
         cachedClassBuilders.remove(element.enclosingClass);
 
         nativeEmitter.cachedBuilders.remove(element.enclosingClass);
 
       }
     }
   }
 }