Expose AppUi from devil utils in browser

telemetry/telemetry/internal/backends/chrome/android_browser_backend.py

 # Copyright 2013 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 logging
 import subprocess
 
 from telemetry.core import exceptions
 from telemetry.internal.platform import android_platform_backend as \
   android_platform_backend_module
@@ skipping 49 matching lines @@
     self.platform_backend.SetDebugApp(self._backend_settings.package)
 
   @property
   def log_file_path(self):
     return None
 
   @property
   def device(self):
     return self.platform_backend.device
 
+  @property
+  def supports_app_ui_interactions(self):
+    return True
+
+  @property
+  def app_ui(self):
+    return app_ui.AppUi(self.device, package=self.package)

[perezju, 2017/04/05 08:46:44]

Can you cache the value after its first use as in:
https://github.com/catapult-project/catapult/blob/master/telemetry/telemetry/...

Also make it a regular method (not property) here. 

[ssid, 2017/04/13 20:07:39]

Done.

+
   def _StopBrowser(self):
     # Note: it's important to stop and _not_ kill the browser app, since
     # stopping also clears the app state in Android's activity manager.
     self.platform_backend.StopApplication(self._backend_settings.package)
 
   def Start(self):
     self.device.adb.Logcat(clear=True)
     if self.browser_options.startup_url:
       url = self.browser_options.startup_url
     elif self.browser_options.profile_dir:
@@ skipping 164 matching lines @@
     return None
 
   def GetAllMinidumpPaths(self):
     return None
 
   def GetAllUnsymbolizedMinidumpPaths(self):
     return None
 
   def SymbolizeMinidump(self, minidump_path):
     return None