Revert of telemetry: Remove command line args from page test

tools/telemetry/telemetry/page/page_test.py

Index: tools/telemetry/telemetry/page/page_test.py
diff --git a/tools/telemetry/telemetry/page/page_test.py b/tools/telemetry/telemetry/page/page_test.py
index 081ea9884cee6838cc335843bf2e1c508c2a9531..478f4a2ba2d0cea964f6718e9c6dc2e22716639d 100644
--- a/tools/telemetry/telemetry/page/page_test.py
+++ b/tools/telemetry/telemetry/page/page_test.py
@@ -2,6 +2,7 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+from telemetry.core import command_line
 from telemetry.page import test_expectations
 from telemetry.page.actions import action_runner as action_runner_module
 
@@ -22,7 +23,7 @@
   designed-for problem."""
 
 
-class PageTest(object):
+class PageTest(command_line.Command):
   """A class styled on unittest.TestCase for creating page-specific tests.
 
   Test should override ValidateAndMeasurePage to perform test
@@ -34,6 +35,19 @@
              'document.body.children.length')
          results.AddValue(scalar.ScalarValue(
              page, 'body_children', 'count', body_child_count))
+
+  The class also provide hooks to add test-specific options. Here is
+  an example:
+
+     class BodyChildElementMeasurement(PageTest):
+       def AddCommandLineArgs(parser):
+         parser.add_option('--element', action='store', default='body')
+
+       def ValidateAndMeasurePage(self, page, tab, results):
+         body_child_count = tab.EvaluateJavaScript(
+             'document.querySelector('%s').children.length')
+         results.AddValue(scalar.ScalarValue(
+             page, 'children', 'count', child_count))
 
   Args:
     action_name_to_run: This is the method name in telemetry.page.Page
@@ -48,6 +62,8 @@
         is_action_name_to_run_optional is True, otherwise the page
         will fail.
   """
+
+  options = {}
 
   def __init__(self,
                action_name_to_run='',
@@ -82,6 +98,10 @@
     # _exit_requested is set to true when the test requests an early exit.
     self._exit_requested = False
 
+  @classmethod
+  def SetArgumentDefaults(cls, parser):
+    parser.set_defaults(**cls.options)
+
   @property
   def discard_first_result(self):
     """When set to True, the first run of the test is discarded.  This is
@@ -117,6 +137,11 @@
   @max_failures.setter
   def max_failures(self, count):
     self._max_failures = count
+
+  def Run(self, args):
+    # Define this method to avoid pylint errors.
+    # TODO(dtu): Make this actually run the test with args.page_set.
+    pass
 
   def RestartBrowserBeforeEachPage(self):
     """ Should the browser be restarted for the page?