Make credential_path a page attribute instead of page_set attribute.

tools/telemetry/telemetry/util/classes.py

Index: tools/telemetry/telemetry/util/classes.py
diff --git a/tools/telemetry/telemetry/util/classes.py b/tools/telemetry/telemetry/util/classes.py
new file mode 100644
index 0000000000000000000000000000000000000000..0f90a06895fd572c4437f6bc58f7f768ba0a6e9b
--- /dev/null
+++ b/tools/telemetry/telemetry/util/classes.py
@@ -0,0 +1,22 @@
+# Copyright 2014 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 inspect
+
+
+def IsDirectlyConstructable(cls):
+  """Returns True if instance of |cls| can be construct without arguments."""
+  assert inspect.isclass(cls)
+  if not hasattr(cls, '__init__'):
+    # Case |class A: pass|.
+    return True
+  if cls.__init__ is object.__init__:
+    # Case |class A(object): pass|.
+    return True
+  # Case |class (object):| with |__init__| other than |object.__init__|.
+  args, _, _, defaults = inspect.getargspec(cls.__init__)
+  if defaults is None:
+    defaults = ()
+  # Return true if |self| is only arg without a default.
+  return len(args) == len(defaults) + 1