[Telemetry] Include debugging info when foreground tab is missing

telemetry/telemetry/core/exceptions.py

 # Copyright 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 import logging
 import sys
 
 
 class Error(Exception):
   """Base class for Telemetry exceptions."""
 
@@ skipping 114 matching lines @@
     super(BrowserGoneException, self).__init__(app, msg)
 
 
 class BrowserConnectionGoneException(BrowserGoneException):
   """Represents a browser that still exists but cannot be reached."""
 
   def __init__(self, app, msg='Browser exists but the connection is gone'):
     super(BrowserConnectionGoneException, self).__init__(app, msg)
 
 
+class TabMissingError(Error):
+  """Represents an error when an expected browser tab is not found."""
+
+
 class ProcessGoneException(Error):
   """Represents a process that no longer exists for an unknown reason."""
 
 
 class IntentionalException(Error):
   """Represent an exception raised by a unittest which is not printed."""
 
 
 class InitializationError(Error):
 
@@ skipping 37 matching lines @@
 class UnknownPackageError(Error):
   """Represents an exception when encountering an unsupported Android APK."""
 
 
 class PackageDetectionError(Error):
   """Represents an error when parsing an Android APK's package."""
 
 
 class AndroidDeviceParsingError(Error):
   """Represents an error when parsing output from an android device."""