Use new Background method in memory perf test.

tools/perf/page_sets/memory_top_10_mobile.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.
 
 import re
 
 from telemetry.page import page as page_module
 from telemetry.page import shared_page_state
 from telemetry import story
 
-from devil.android.sdk import intent # pylint: disable=import-error
 from devil.android.sdk import keyevent # pylint: disable=import-error
 
 from page_sets import top_10_mobile
 
 
 class MemoryMeasurementPage(page_module.Page):
   """Abstract class for measuring memory on a story unit."""
 
   _PHASE = NotImplemented
 
@@ skipping 22 matching lines @@
 
   _PHASE = 'background'
 
   def __init__(self, story_set, name):
     super(BackgroundPage, self).__init__(story_set, name, 'about:blank')
 
   def RunPageInteractions(self, action_runner):
     action_runner.tab.WaitForDocumentReadyStateToBeComplete()
 
     # Launch clock app, pushing Chrome to the background.
-    android_platform = action_runner.tab.browser.platform
-    android_platform.LaunchAndroidApplication(
-        intent.Intent(package='com.google.android.deskclock',
-                      activity='com.android.deskclock.DeskClock'),
-        app_has_webviews=False)
+    android_browser = action_runner.tab.browser
+    android_browser.Background()
 
     # Take measurement.
     action_runner.MeasureMemory(self.story_set.DETERMINISTIC_MODE)
 
     # Go back to Chrome.
-    android_platform.android_action_runner.InputKeyEvent(keyevent.KEYCODE_BACK)
+    android_browser.platform.android_action_runner.InputKeyEvent(
+        keyevent.KEYCODE_BACK)
 
 
 class MemoryTop10Mobile(story.StorySet):
   """User story to measure foreground/background memory in top 10 mobile."""
   DETERMINISTIC_MODE = True
 
   def __init__(self):
     super(MemoryTop10Mobile, self).__init__(
         archive_data_file='data/memory_top_10_mobile.json',
         cloud_storage_bucket=story.PARTNER_BUCKET)
 
     for url in top_10_mobile.URL_LIST:
       # We name pages so their foreground/background counterparts are easy
       # to identify. For example 'http://google.com' becomes
       # 'http_google_com' and 'after_http_google_com' respectively.
       name = re.sub(r'\W+', '_', url)
       self.AddStory(ForegroundPage(self, name, url))
       self.AddStory(BackgroundPage(self, 'after_' + name))
 
 
 class MemoryTop10MobileRealistic(MemoryTop10Mobile):
   """Top 10 mobile user story in realistic mode.
 
   This means, in particular, neither forced GCs nor clearing caches.
   """
   DETERMINISTIC_MODE = False