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

lib/src/formatter_exception.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.formatter_exception;
-
-import 'package:analyzer/analyzer.dart';
-import 'package:source_span/source_span.dart';
-
-/// Thrown when one or more errors occurs while parsing the code to be
-/// formatted.
-class FormatterException implements Exception {
-  /// The [AnalysisError]s that occurred.
-  final List<AnalysisError> errors;
-
-  /// Creates a new FormatterException with an optional error [message].
-  const FormatterException(this.errors);
-
-  /// Creates a human-friendly representation of the analysis errors.
-  String message({bool color}) {
-    var buffer = new StringBuffer();
-    buffer.writeln("Could not format because the source could not be parsed:");
-
-    // In case we get a huge series of cascaded errors, just show the first few.
-    var shownErrors = errors;
-    if (errors.length > 10) shownErrors = errors.take(10);
-
-    for (var error in shownErrors) {
-      var source = error.source.contents.data;
-
-      // If the parse error is for something missing from the end of the file,
-      // the error position will go past the end of the source. In that case,
-      // just pad the source with spaces so we can report it nicely.
-      if (error.offset + error.length > source.length) {
-        source += " " * (error.offset + error.length - source.length);
-      }
-
-      var file = new SourceFile(source, url: error.source.fullName);
-      var span = file.span(error.offset, error.offset + error.length);
-      if (buffer.isNotEmpty) buffer.writeln();
-      buffer.write(span.message(error.message, color: color));
-    }
-
-    if (shownErrors.length != errors.length) {
-      buffer.writeln();
-      buffer.write("(${errors.length - shownErrors.length} more errors...)");
-    }
-
-    return buffer.toString();
-  }
-
-  String toString() => message();
-}