Enable type inference when using mirrors.

sdk/lib/_internal/compiler/implementation/js_backend/backend.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.
 
 part of js_backend;
 
 class JavaScriptItemCompilationContext extends ItemCompilationContext {
   final Set<HInstruction> boundsChecked;
 
   JavaScriptItemCompilationContext()
@@ skipping 353 matching lines @@
         new MinifyNamer(compiler) :
         new Namer(compiler);
   }
 
   bool canBeUsedForGlobalOptimizations(Element element) {
     if (element.isParameter()
         || element.isFieldParameter()
         || element.isField()) {
       element = element.enclosingElement;
     }
-    return !helpersUsed.contains(element.declaration);
+    element = element.declaration;
+    return !isNeededForReflection(element) && !helpersUsed.contains(element);
   }
 
   bool isInterceptorClass(ClassElement element) {
     if (element == null) return false;
     if (Elements.isNativeOrExtendsNative(element)) return true;
     if (interceptedClasses.contains(element)) return true;
     if (classesMixedIntoNativeClasses.contains(element)) return true;
     return false;
   }
 
@@ skipping 1304 matching lines @@
     copy(constant.values);
     copy(constant.protoValue);
     copy(constant);
   }
 
   void visitConstructed(ConstructedConstant constant) {
     copy(constant.fields);
     copy(constant);
   }
 }