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

pkg/compiler/bin/resolver.dart

Index: pkg/compiler/bin/resolver.dart
diff --git a/pkg/compiler/bin/resolver.dart b/pkg/compiler/bin/resolver.dart
index c75d394975ab9325f480db3c0aea34c05216efd4..d5b56da25d3c58093f18c0855fcf61658755ec48 100644
--- a/pkg/compiler/bin/resolver.dart
+++ b/pkg/compiler/bin/resolver.dart
@@ -45,7 +45,8 @@ main(var argv) async {
       : 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);