Add ScopeInfo class for variable information that doesn't actually involve closures.

tests/compiler/dart2js/closure/closure_test.dart

 // Copyright (c) 2017, 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 'dart:io';
 import 'package:async_helper/async_helper.dart';
 import 'package:compiler/src/closure.dart';
 import 'package:compiler/src/common.dart';
 import 'package:compiler/src/compiler.dart';
 import 'package:compiler/src/diagnostics/diagnostic_listener.dart';
@@ skipping 110 matching lines @@
   String computeMemberValue(ir.Member member) {
     // TODO(johnniwinther,efortuna): Collect data for the member
     // (has thisLocal, has box, etc.).
     return null;
   }
 }
 
 /// Compute a string representation of the data stored for [local] in [info].
 String computeLocalValue(ClosureRepresentationInfo info, Local local) {
   StringBuffer sb = new StringBuffer();
-  if (info.variableIsUsedInTryOrSync(local)) {
+  if (info.variablesUsedInTryOrSync.contains(local)) {
     sb.write('inTry');
   }
   // TODO(johnniwinther,efortuna): Add more info (captured, boxed etc.).
   return sb.toString();
 }