Fix analyzer warnings for https://codereview.chromium.org/1642493002

pkg/compiler/lib/src/cps_ir/cps_ir_builder_task.dart

 // Copyright (c) 2013, 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 dart2js.ir_builder_task;
 
 import '../closure.dart' as closure;
 import '../common.dart';
 import '../common/names.dart' show
     Names,
@@ skipping 900 matching lines @@
       //    t1 = setRuntimeTypeInfo(allocation, TypeExpression($E));
       //    return Refinement(t1, <JSArray>);
       //
       assert(parameters.length == 1 || parameters.length == 2);
       ir.Primitive allocation = irBuilder.buildLocalGet(parameters[0]);
       ClassElement classElement = element.enclosingElement;
 
       // Only call setRuntimeTypeInfo if JSArray requires the type parameter.
       if (requiresRuntimeTypes) {
         assert(parameters.length == 2);
+        closure.TypeVariableLocal typeParameter = parameters[1];
         ir.Primitive typeArgument =
-            irBuilder.buildTypeVariableAccess(parameters[1].typeVariable);
+            irBuilder.buildTypeVariableAccess(typeParameter.typeVariable);
 
         ir.Primitive typeInformation = irBuilder.addPrimitive(
             new ir.TypeExpression(ir.TypeExpressionKind.INSTANCE,
                                   element.enclosingClass.thisType,
                                   <ir.Primitive>[typeArgument]));
 
-        Element helper = helpers.setRuntimeTypeInfo;
+        MethodElement helper = helpers.setRuntimeTypeInfo;
         CallStructure callStructure = CallStructure.TWO_ARGS;
         Selector selector = new Selector.call(helper.memberName, callStructure);
         allocation = irBuilder.buildInvokeStatic(
             helper, selector, <ir.Primitive>[allocation, typeInformation],
             sourceInformationBuilder.buildGeneric(node));
       }
 
       ir.Primitive refinement = irBuilder.addPrimitive(
           new ir.Refinement(allocation, typeMaskSystem.arrayType));
 
@@ skipping 2949 matching lines @@
   }
 
   Element get closureConverter {
     return _backend.helpers.closureConverter;
   }
 
   void addNativeMethod(FunctionElement function) {
     _backend.emitter.nativeEmitter.nativeMethods.add(function);
   }
 }