[Telemetry] Factor out common logic between inspector backend lists.

tools/telemetry/telemetry/core/extension_dict.py

Index: tools/telemetry/telemetry/core/extension_dict.py
diff --git a/tools/telemetry/telemetry/core/extension_dict.py b/tools/telemetry/telemetry/core/extension_dict.py
index a2221dacd71efa342117857a994bcfcdecc64f38..c4659c75dc6a722b622506054b396f60513657d3 100644
--- a/tools/telemetry/telemetry/core/extension_dict.py
+++ b/tools/telemetry/telemetry/core/extension_dict.py
@@ -1,28 +1,28 @@
 # Copyright (c) 2012 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.
+
 from telemetry.core import extension_to_load
 
+
 class ExtensionDict(object):
-  """Dictionary of ExtensionPage instances, with extension_id as key"""
+  """Dictionary of ExtensionPage instances, with extension_id as key."""
 
-  def __init__(self, extension_dict_backend):
-    self._extension_dict_backend = extension_dict_backend
+  def __init__(self, extension_backend):
+    self._extension_backend = extension_backend
 
   def __getitem__(self, load_extension):
     """Given an ExtensionToLoad instance, returns the corresponding
     ExtensionPage instance."""
     if not isinstance(load_extension, extension_to_load.ExtensionToLoad):
-      raise Exception("Input param must be of type ExtensionToLoad")
-    return self._extension_dict_backend.__getitem__(
-        load_extension.extension_id)
+      raise TypeError("Input param must be of type ExtensionToLoad")
+    return self._extension_backend[load_extension.extension_id]
 
   def __contains__(self, load_extension):
     """Checks if this ExtensionToLoad instance has been loaded"""
     if not isinstance(load_extension, extension_to_load.ExtensionToLoad):
-      raise Exception("Input param must be of type ExtensionToLoad")
-    return self._extension_dict_backend.__contains__(
-        load_extension.extension_id)
+      raise TypeError("Input param must be of type ExtensionToLoad")
+    return load_extension.extension_id in self._extension_backend
 
   def keys(self):
-    return self._extension_dict_backend.GetExtensionIds()
+    return self._extension_backend.keys()