Roll Observatory packages and add a roll script

packages/which/test/util.dart

+
+library which.test.util;
+
+import 'dart:io';
+
+import 'package:mockito/mockito.dart';
+import 'package:path/path.dart' as path;
+import 'package:which/src/candidate_paths.dart';
+
+getPosixCandidatePaths(String command, String pathVar, String current) {
+  var env = {
+    'PATH': pathVar
+  };
+  var isWindows = false;
+  var context = new path.Context(style: path.Style.posix, current: current);
+
+  return getCandidatePaths(command, env, isWindows, context);
+}
+
+getWindowsCandidatePaths(String command, String pathVar, String pathExtVar, String current) {
+  var env = {
+    'PATH': pathVar,
+    'PATHEXT': pathExtVar
+  };
+  var isWindows = true;
+  var context = new path.Context(style: path.Style.windows, current: current);
+
+  return getCandidatePaths(command, env, isWindows, context);
+}
+
+class MockFileStat extends Mock implements FileStat {
+
+  MockFileStat();
+
+  noSuchMethod(i) => super.noSuchMethod(i);
+}
+
+int parseBinary(String b) => int.parse(b, radix: 2);