Don't dump a stack trace on the user if the formatter had bad output.

lib/src/io.dart

 // Copyright (c) 2014, 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 dart_style.src.io;
 
 import 'dart:io';
 
 import 'package:path/path.dart' as p;
 
 import 'dart_formatter.dart';
-import 'formatter_exception.dart';
+import 'exceptions.dart';
 import 'formatter_options.dart';
 import 'source_code.dart';
 
 /// Runs the formatter on every .dart file in [path] (and its subdirectories),
 /// and replaces them with their formatted output.
 ///
 /// Returns `true` if successful or `false` if an error occurred in any of the
 /// files.
 bool processDirectory(FormatterOptions options, Directory directory) {
   options.reporter.showDirectory(directory.path);
@@ skipping 51 matching lines @@
     options.reporter.beforeFile(file, label);
     var output = formatter.formatSource(source);
     options.reporter
         .afterFile(file, label, output, changed: source.text != output.text);
     return true;
   } on FormatterException catch (err) {
     var color = Platform.operatingSystem != "windows" &&
         stdioType(stderr) == StdioType.TERMINAL;
 
     stderr.writeln(err.message(color: color));
+  } on UnexpectedOutputException catch (err) {
+    stderr.writeln('''Hit a bug in the formatter when formatting $label.
+$err
+Please report at github.com/dart-lang/dart_style/issues.''');
   } catch (err, stack) {
     stderr.writeln('''Hit a bug in the formatter when formatting $label.
-Please report at: github.com/dart-lang/dart_style/issues
+Please report at github.com/dart-lang/dart_style/issues.
 $err
 $stack''');
   }
 
   return false;
 }