Revert of webrtc: run tests in the checkout directory

scripts/slave/recipe_modules/webrtc/api.py

Index: scripts/slave/recipe_modules/webrtc/api.py
diff --git a/scripts/slave/recipe_modules/webrtc/api.py b/scripts/slave/recipe_modules/webrtc/api.py
index 3ea92f51b22d5edfa60b34f44ddae8fedd58032a..d6b333f18e54d979868af1cc5bbd25e69da2817c 100644
--- a/scripts/slave/recipe_modules/webrtc/api.py
+++ b/scripts/slave/recipe_modules/webrtc/api.py
@@ -181,7 +181,11 @@
     Args:
       test_suite: The name of the test suite.
     """
-    with self.m.step.context({'cwd': self.m.path['checkout']}):
+    context = {}
+    if self._working_dir:
+      context['cwd'] = self._working_dir
+
+    with self.m.step.context(context):
       if self.c.use_isolate:
         self.m.isolate.remove_build_metadata()
         self.m.isolate.isolate_tests(self.m.chromium.output_dir,