test.dart: Find cdb.exe automatically from depot_tools when running Windows tests

tools/testing/dart/test_configurations.dart

 // Copyright (c) 2012, 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_configurations;
 
 import "dart:async";
+import 'dart:convert';
 import 'dart:io';
 import "dart:math" as math;
 
 import 'android.dart';
 import "browser_controller.dart";
 import "co19_test_config.dart";
 import "http_server.dart";
 import "path.dart";
 import "test_progress.dart";
 import "test_runner.dart";
@@ skipping 29 matching lines @@
   new Path('tests/language'),
   new Path('tests/language_strong'),
   new Path('tests/lib'),
   new Path('tests/lib_strong'),
   new Path('tests/standalone'),
   new Path('tests/utils'),
   new Path('utils/tests/css'),
   new Path('utils/tests/peg'),
 ];
 
+// This file is created by gclient runhooks.
+final VS_TOOLCHAIN_FILE = new Path("build/win_toolchain.json");
+
 Future testConfigurations(List<Map> configurations) async {
   var startTime = new DateTime.now();
   // Extract global options from first configuration.
   var firstConf = configurations[0];
   var maxProcesses = firstConf['tasks'];
   var progressIndicator = firstConf['progress'];
   BuildbotProgressIndicator.stepName = firstConf['step_name'];
   var verbose = firstConf['verbose'];
   var printTiming = firstConf['time'];
   var listTests = firstConf['list'];
@@ skipping 220 matching lines @@
   });
   if (needsAdbDevicePool) {
     adbDevicePool = await AdbDevicePool.create();
   }
 
   // Start all the HTTP servers required before starting the process queue.
   if (!serverFutures.isEmpty) {
     await Future.wait(serverFutures);
   }
 
+  if (Platform.isWindows) {
+    // When running tests on Windows, use cdb from depot_tools to dump
+    // stack traces of tests timing out.

[Bill Hesse, 2017/03/01 13:45:56]

It would be good to put this in a try block, so it doesn't kill the test run if
it fails.  For example, if gclient sync hasn't been run.

[Florian Schneider, 2017/03/02 22:56:08]

I'll add one here.

+    var text = await new File(VS_TOOLCHAIN_FILE.toNativePath()).readAsString();
+    firstConf['win_sdk_path'] = JSON.decode(text)['win_sdk'];
+  }
+
   // [firstConf] is needed here, since the ProcessQueue needs to know the
   // settings of 'noBatch' and 'local_ip'
   new ProcessQueue(
       firstConf,
       maxProcesses,
       maxBrowserProcesses,
       startTime,
       testSuites,
       eventListener,
       allTestsFinished,
       verbose,
       recordingPath,
       recordingOutputPath,
       adbDevicePool);
 }