Prefer "dart:" URLs to "package:" URLs.

lib/source_map_stack_trace.dart

 // Copyright (c) 2015, 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 source_map_stack_trace;
 
 import 'package:path/path.dart' as p;
 import 'package:source_maps/source_maps.dart';
 import 'package:stack_trace/stack_trace.dart';
 
@@ skipping 43 matching lines @@
 
     // Subtract 1 because stack traces use 1-indexed lines and columns and
     // source maps uses 0-indexed.
     var span = sourceMap.spanFor(frame.line - 1, column - 1);
 
     // If we can't find a source span, ignore the frame. It's probably something
     // internal that the user doesn't care about.
     if (span == null) return null;
 
     var sourceUrl = span.sourceUrl.toString();
-    if (packageRoot != null && p.url.isWithin(packageRoot, sourceUrl)) {
+    if (sdkRoot != null && p.url.isWithin(sdkLib, sourceUrl)) {
+      sourceUrl = "dart:" + p.url.relative(sourceUrl, from: sdkLib);
+    } else if (packageRoot != null && p.url.isWithin(packageRoot, sourceUrl)) {
       sourceUrl = "package:" +
           p.url.relative(sourceUrl, from: packageRoot);
-    } else if (sdkRoot != null && p.url.isWithin(sdkLib, sourceUrl)) {
-      sourceUrl = "dart:" + p.url.relative(sourceUrl, from: sdkLib);
     }
 
     return new Frame(
         Uri.parse(sourceUrl),
         span.start.line + 1,
         span.start.column + 1,
         // If the dart2js output is minified, there's no use trying to prettify
         // its member names. Use the span's identifier if available, otherwise
         // use the minified member name.
         minified
@@ skipping 22 matching lines @@
       .replaceAll(new RegExp(r"[a-zA-Z_0-9]+\$"), "")
       // Get rid of the static method prefix. The class name also exists in the
       // invocation, so we're not getting rid of any information.
       .replaceAll(new RegExp(r"^[a-zA-Z_0-9]+.static."), "")
       // Convert underscores after identifiers to dots. This runs the risk of
       // incorrectly converting members that contain underscores, but those are
       // contrary to the style guide anyway.
       .replaceAllMapped(new RegExp(r"([a-zA-Z0-9]+)_"),
           (match) => match[1] + ".");
 }