pkg/stack_trace: use List.unmodifiable when possible

lib/src/trace.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.
 
-import 'dart:collection';
 import 'dart:math' as math;
 
 import 'chain.dart';
 import 'frame.dart';
 import 'lazy_trace.dart';
 import 'unparsed_frame.dart';
 import 'utils.dart';
 import 'vm_trace.dart';
 
 final _terseRegExp = new RegExp(r"(-patch)?([/\\].*)?$");
@@ skipping 182 matching lines @@
   Trace.parseFriendly(String trace)
       : this(trace.isEmpty
             ? []
             : trace.trim().split("\n")
                 // Filter out asynchronous gaps from [Chain]s.
                 .where((line) => !line.startsWith('====='))
                 .map((line) => new Frame.parseFriendly(line)));
 
   /// Returns a new [Trace] comprised of [frames].
   Trace(Iterable<Frame> frames)
-      : frames = new UnmodifiableListView<Frame>(frames.toList());
+      : frames = new List<Frame>.unmodifiable(frames);
 
   /// Returns a VM-style [StackTrace] object.
   ///
   /// The return value's [toString] method will always return a string
   /// representation in the Dart VM's stack trace format, regardless of what
   /// platform is being used.
   StackTrace get vmTrace => new VMTrace(frames);
 
   /// Returns a terser version of [this].
   ///
@@ skipping 66 matching lines @@
     var longest = frames.map((frame) => frame.location.length)
         .fold(0, math.max);
 
     // Print out the stack trace nicely formatted.
     return frames.map((frame) {
       if (frame is UnparsedFrame) return "$frame\n";
       return '${padRight(frame.location, longest)}  ${frame.member}\n';
     }).join();
   }
 }