Improve error reporting: use colors and associate the appropiate file with

pkg/compiler/bin/resolver.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 'dart:io';
 
 import 'package:args/args.dart';
 import 'package:compiler/src/apiimpl.dart';
 import 'package:compiler/src/filenames.dart';
 import 'package:compiler/src/null_compiler_output.dart';
@@ skipping 27 matching lines @@
       resolveOnly: true,
       resolutionInputs: resolutionInputs,
       packagesDiscoveryProvider: findPackages);
 
   var bazelSearchPaths = args['bazel-paths'];
   var inputProvider = bazelSearchPaths != null
       ? new BazelInputProvider(bazelSearchPaths)
       : new CompilerSourceFileProvider();
 
   var outputProvider = const NullCompilerOutput();
-  var diagnostics = new FormattingDiagnosticHandler(inputProvider);
+  var diagnostics = new FormattingDiagnosticHandler(inputProvider)
+    ..enableColors = true;
   var compiler =
       new CompilerImpl(inputProvider, outputProvider, diagnostics, options);
 
   if (args.rest.isEmpty) {
     print('missing input files');
     exit(1);
   }
 
   var inputs = args.rest
       .map((uri) => currentDirectory.resolve(nativeToUriPath(uri)))
@@ skipping 17 matching lines @@
       inputs.map((lib) => compiler.libraryLoader.lookupLibrary(lib)).toList();
 
   var serializer =
       compiler.serialization.createSerializer(librariesToSerialize);
   var text = serializer.toText(const JsonSerializationEncoder());
 
   var outFile = args['out'] ?? 'out.data';
 
   await new File(outFile).writeAsString(text);
 }