Fix cros telemetry bustage.

Regression introduced by crrev.com/216268
Symptom is errors like:
TypeError("argument of type 'NoneType' is not iterable",)

BUG=270148
TEST=manual
R=tonyg@chromium.org

Review URL: https://codereview.chromium.org/22879002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@217026 0039d316-1c4b-4281-b951-d872f2087c98

tools/telemetry/telemetry/core/chrome/cros_browser_backend.py

@@ -140,14 +140,14 @@ class CrOSBrowserBackend(chrome_browser_backend.ChromeBrowserBackend):
   @property
   def pid(self):
     result = self._GetChromeProcess()
-    if 'pid' in result:
+    if result and 'pid' in result:
       return result['pid']
     return None
 
   @property
   def browser_directory(self):
     result = self._GetChromeProcess()
-    if 'path' in result:
+    if result and 'path' in result:
       return result['path']
     return None