Revert "Improving relative path support."

runtime/bin/path_impl.dart

Index: runtime/bin/path_impl.dart
diff --git a/runtime/bin/path_impl.dart b/runtime/bin/path_impl.dart
index bd9cb48243e73dc793bfabb35fbe247e14f03dce..9c7e43825e96a84a26c092c59c7adcfe4f8d816b 100644
--- a/runtime/bin/path_impl.dart
+++ b/runtime/bin/path_impl.dart
@@ -49,34 +49,10 @@ class _Path implements Path {
       if (_path[base._path.length] == '/') {
         return new Path(_path.substring(base._path.length + 1));
       }
-    } else if (base.isAbsolute && isAbsolute) {
-      List<String> baseSegments = base.canonicalize().segments();
-      List<String> pathSegments = canonicalize().segments();
-      int common = 0;
-      int length = min(pathSegments.length, baseSegments.length);
-      while (common < length && pathSegments[common] == baseSegments[common]) {
-        common++;
-      }
-      final sb = new StringBuffer();
-
-      for (int i = common + 1; i < baseSegments.length; i++) {
-        sb.add('../');
-      }
-      if (base.hasTrailingSeparator) {
-        sb.add('../');
-      }
-      for (int i = common; i < pathSegments.length - 1; i++) {
-        sb.add('${pathSegments[i]}/');
-      }
-      sb.add('${pathSegments.last()}');
-      if (_path.hasTrailingSeparator) {
-        sb.add('/');
-      }
-      return new Path(sb.toString());
     }
     throw new NotImplementedException(
       "Unimplemented case of Path.relativeTo(base):\n"
-      "  Only absolute paths are handled at present.\n"
+      "  Only absolute paths with strict containment are handled at present.\n"
       "  Arguments: $_path.relativeTo($base)");
   }