Telemetry: Update exception handling in FastNavigationProfileExtender.

tools/perf/profile_creators/profile_extender.py

Index: tools/perf/profile_creators/profile_extender.py
diff --git a/tools/perf/profile_creators/profile_extender.py b/tools/perf/profile_creators/profile_extender.py
index b1dccfa68bb897cbcf05a852af9dd2ebee112306..a623a94ef34ac06ee9440008695ef0212fa698e5 100644
--- a/tools/perf/profile_creators/profile_extender.py
+++ b/tools/perf/profile_creators/profile_extender.py
@@ -87,6 +87,13 @@ class ProfileExtender(object):
       self._browser.Close()
       self._browser = None
 
+  def VerifyProfileWasExtended(self):
+    """Verifies that the profile was correctly extended.
+
+    Can be overridden by subclasses.
+    """
+    pass
+
   def FetchWebPageReplayArchives(self):
     """Fetches the web page replay archives.