Fix dart2js warnings and add test to ensure it stays clean.

pkg/compiler/lib/src/ssa/builder_kernel.dart

 // Copyright (c) 2016, 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.
 
 import 'package:kernel/ast.dart' as ir;
 
 import '../closure.dart';
 import '../common.dart';
 import '../common/codegen.dart' show CodegenRegistry, CodegenWorkItem;
 import '../common/names.dart';
@@ skipping 10 matching lines @@
 import '../elements/resolution_types.dart';
 import '../io/source_information.dart';
 import '../js/js.dart' as js;
 import '../js_backend/backend.dart' show JavaScriptBackend;
 import '../kernel/kernel.dart';
 import '../native/native.dart' as native;
 import '../resolution/tree_elements.dart';
 import '../tree/dartstring.dart';
 import '../tree/nodes.dart' show Node;
 import '../types/masks.dart';
-import '../universe/call_structure.dart' show CallStructure;
 import '../universe/selector.dart';
 import '../universe/side_effects.dart' show SideEffects;
-import '../universe/use.dart' show DynamicUse, StaticUse;
+import '../universe/use.dart' show DynamicUse;
 import '../world.dart';
 import 'graph_builder.dart';
 import 'jump_handler.dart';
 import 'kernel_ast_adapter.dart';
 import 'kernel_string_builder.dart';
 import 'locals_handler.dart';
 import 'loop_handler.dart';
 import 'nodes.dart';
 import 'ssa_branch_builder.dart';
 import 'switch_continue_analysis.dart';
@@ skipping 2843 matching lines @@
     return;
   }
 
   bool _isInterfaceWithNoDynamicTypes(ir.DartType type) {
     bool isMethodTypeVariableType(ir.DartType typeArgType) {
       return (typeArgType is ir.TypeParameterType &&
           typeArgType.parameter.parent is ir.FunctionNode);
     }
 
     return type is ir.InterfaceType &&
-        (type as ir.InterfaceType).typeArguments.any(
-            (ir.DartType typeArgType) =>
-                typeArgType is! ir.DynamicType &&
-                typeArgType is! ir.InvalidType &&
-                !isMethodTypeVariableType(type));
+        type.typeArguments.any((ir.DartType typeArgType) =>
+            typeArgType is! ir.DynamicType &&
+            typeArgType is! ir.InvalidType &&
+            !isMethodTypeVariableType(type));
   }
 
   @override
   void visitThrow(ir.Throw throwNode) {
     _visitThrowExpression(throwNode.expression);
     if (isReachable) {
       handleInTryStatement();
       push(new HThrowExpression(pop(), null));
       isReachable = false;
     }
@@ skipping 315 matching lines @@
     enterBlock.setBlockFlow(
         new HTryBlockInformation(
             kernelBuilder.wrapStatementGraph(bodyGraph),
             exception,
             kernelBuilder.wrapStatementGraph(catchGraph),
             kernelBuilder.wrapStatementGraph(finallyGraph)),
         exitBlock);
     kernelBuilder.inTryStatement = previouslyInTryStatement;
   }
 }