Fix warning

lib/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.
 
 class InvocationInfo {
   int parameterCount = -1;
   List<HType> providedTypes;
   List<Element> compiledFunctions;
 
   InvocationInfo(HInvoke node, HTypeMap types)
@@ skipping 43 matching lines @@
       }
       compiledFunctions.clear();
     }
     // If all information is lost no need to keep it around.
     if (allUnknown) clearTypeInformation();
   }
 
   addCompiledFunction(FunctionElement function) =>
       compiledFunctions.add(function);
 
-  void clearTypeInformation() => providedTypes = null;
+  void clearTypeInformation() { providedTypes = null; }
   bool get hasTypeInformation() => providedTypes != null;
 
 }
 
 class ReturnInfo {
   HType returnType;
   List<Element> compiledFunctions;
 
   ReturnInfo(HType this.returnType)
       : compiledFunctions = new List<Element>();
@@ skipping 336 matching lines @@
   HType optimisticReturnTypesWithRecompilationOnTypeChange(
       FunctionElement caller, FunctionElement callee) {
     returnInfo.putIfAbsent(callee, () => new ReturnInfo.unknownType());
     ReturnInfo info = returnInfo[callee];
     if (info.returnType != HType.UNKNOWN && caller != null) {
       info.addCompiledFunction(caller);
     }
     return info.returnType;
   }
 }