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

tools/testing/dart/test_configurations.dart

Index: tools/testing/dart/test_configurations.dart
diff --git a/tools/testing/dart/test_configurations.dart b/tools/testing/dart/test_configurations.dart
index 9418bd7d083c2ad0593f82aa16c933cef96cc967..8944af89200a712423cae6161fd80bc9da63a0b4 100644
--- a/tools/testing/dart/test_configurations.dart
+++ b/tools/testing/dart/test_configurations.dart
@@ -5,6 +5,7 @@
 library test_configurations;
 
 import "dart:async";
+import 'dart:convert';
 import 'dart:io';
 import "dart:math" as math;
 
@@ -54,6 +55,9 @@ final TEST_SUITE_DIRECTORIES = [
   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.
@@ -294,6 +298,13 @@ Future testConfigurations(List<Map> configurations) async {
     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(