Make source map location information more readable.

pkg/csslib/test/var_test.dart

 // Copyright (c) 2013, 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 var_test;
 
 import 'package:unittest/unittest.dart';
 import 'testing.dart';
 
 List options = ['--no-colors', '--warnings_as_errors', 'memory'];
@@ skipping 374 matching lines @@
 }
 .test-1 {
   color: #0f0;
 }
 .test-2 {
   color: ;
   background: ;
 }''';
 
   var errorStrings = [
-    'error :5:14: Variable is not defined.\n'
+    'error on line 5, column 14: Variable is not defined.\n'
     '  var-a: var(b);\n'
     '             ^^',
-    'error :6:14: Variable is not defined.\n'
+    'error on line 6, column 14: Variable is not defined.\n'
     '  var-b: var(c);\n'
     '             ^^',
-    'error :9:16: Variable is not defined.\n'
+    'error on line 9, column 16: Variable is not defined.\n'
     '  var-one: var(two);\n'
     '               ^^^^',
-    'error :12:17: Variable is not defined.\n'
+    'error on line 12, column 17: Variable is not defined.\n'
     '  var-four: var(five);\n'
     '                ^^^^^',
-    'error :13:17: Variable is not defined.\n'
+    'error on line 13, column 17: Variable is not defined.\n'
     '  var-five: var(six);\n'
     '                ^^^^',
-    'error :16:18: Variable is not defined.\n'
+    'error on line 16, column 18: Variable is not defined.\n'
     '  var-def-1: var(def-2);\n'
     '                 ^^^^^^',
-    'error :17:18: Variable is not defined.\n'
+    'error on line 17, column 18: Variable is not defined.\n'
     '  var-def-2: var(def-3);\n'
     '                 ^^^^^^',
     ];
 
   var generated = r''':root {
   var-color-background: #f00;
   var-color-foreground: #00f;
   var-a: var(b);
   var-b: var(c);
   var-c: #0f0;
@@ skipping 493 matching lines @@
   test('Expressions var', expressionsVar);
   test('Default value in var()', defaultVar);
   test('CSS Parser only var', parserVar);
   test('Var syntax', testVar);
   test('Indirects', testIndirects);
   test('Forward Refs', undefinedVars);
   test('Less syntax', testLess);
   test('Polyfill', polyfill);
   test('Multi-file', includes);
 }