Add key_idle_power_cases for ensuring idle activity on Android

tools/perf/page_sets/android_screen_restoration_shared_state.py

+# Copyright 2015 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.page import shared_page_state
+
+
+class AndroidScreenRestorationSharedState(shared_page_state.SharedPageState):
+  """ Ensures the screen is on before and after each user story run. """
+
+  def WillRunUserStory(self, page):
+    super(AndroidScreenRestorationSharedState, self).WillRunUserStory(page)
+    self._EnsureScreenOn()
+
+  def DidRunUserStory(self, results):
+    try:
+      super(AndroidScreenRestorationSharedState, self).DidRunUserStory(results)
+    finally:
+      self._EnsureScreenOn()
+
+  def _EnsureScreenOn(self):
+    self.platform.android_action_runner.TurnScreenOn()
+