Make source maps work in the browser.

lib/src/runner/browser/compiler_pool.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 test.util.compiler_pool;
 
 import 'dart:async';
 import 'dart:convert';
 import 'dart:io';
 
@@ skipping 87 matching lines @@
           _printOutputStream(process.stdout, buffer),
           _printOutputStream(process.stderr, buffer),
         ]);
 
         var exitCode = await process.exitCode;
         _processes.remove(process);
         if (_closed) return;
 
         if (buffer.isNotEmpty) print(buffer);
 
-        if (exitCode != 0) {
-          throw new LoadException(dartPath, "dart2js failed.");
-        }
+        if (exitCode != 0) throw new LoadException(dartPath, "dart2js failed.");
+
+        _fixSourceMap(jsPath + '.map');
       });
     });
   }
 
+  // TODO(nweiz): Remove this when sdk#17544 is fixed.
+  /// Fix up the source map at [mapPath] so that it points to absolute file:
+  /// URIs that are resolvable by the browser.
+  void _fixSourceMap(String mapPath) {
+    var map = JSON.decode(new File(mapPath).readAsStringSync());
+    var root = map['sourceRoot'];
+
+    map['sources'] = map['sources'].map((source) {
+      var url = Uri.parse(root + source);
+      if (url.scheme != '' && url.scheme != 'file') return source;
+      if (url.path.endsWith("/runInBrowser.dart")) return "";
+      return p.toUri(mapPath).resolveUri(url).toString();
+    }).toList();
+
+    new File(mapPath).writeAsStringSync(JSON.encode(map));
+  }
+
   /// Sanitizes the bytes emitted by [stream], converts them to text, and writes
   /// them to [buffer].
   Future _printOutputStream(Stream<List<int>> stream, StringBuffer buffer) {
     return sanitizeForWindows(stream)
         .listen((data) => buffer.write(UTF8.decode(data))).asFuture();
   }
 
   /// Closes the compiler pool.
   ///
   /// This kills all currently-running compilers and ensures that no more will
   /// be started. It returns a [Future] that completes once all the compilers
   /// have been killed and all resources released.
   Future close() {
     return _closeMemo.runOnce(() async {
       await Future.wait(_processes.map((process) async {
         process.kill();
         await process.exitCode;
       }));
     });
   }
 }