[Telemetry] Improve Android cycle time.

tools/telemetry/telemetry/core/platform/power_monitor/android_ds2784_power_monitor.py

Index: tools/telemetry/telemetry/core/platform/power_monitor/android_ds2784_power_monitor.py
diff --git a/tools/telemetry/telemetry/core/platform/power_monitor/android_ds2784_power_monitor.py b/tools/telemetry/telemetry/core/platform/power_monitor/android_ds2784_power_monitor.py
index 4d5d350e6605a3e906400b4103b2bac04d329bd2..8b66e89d4dc58900e64bd2eedd846a08a6522999 100644
--- a/tools/telemetry/telemetry/core/platform/power_monitor/android_ds2784_power_monitor.py
+++ b/tools/telemetry/telemetry/core/platform/power_monitor/android_ds2784_power_monitor.py
@@ -23,7 +23,6 @@ class DS2784PowerMonitor(power_monitor.PowerMonitor):
     super(DS2784PowerMonitor, self).__init__()
     self._device = device
     self._powermonitor_process_port = None
-    android_prebuilt_profiler_helper.InstallOnDevice(device, 'file_poller')
     self._file_poller_binary = android_prebuilt_profiler_helper.GetDevicePath(
         'file_poller')
 
@@ -43,6 +42,8 @@ class DS2784PowerMonitor(power_monitor.PowerMonitor):
   def StartMonitoringPower(self, browser):
     assert not self._powermonitor_process_port, (
         'Must call StopMonitoringPower().')
+    android_prebuilt_profiler_helper.InstallOnDevice(
+        self._device, 'file_poller')

[qsr, 2014/05/23 09:15:36]

Do you want to cache that you did that already once? As otherwise it will be
called between each page of a test suite, or is the second call mostly free?

[tonyg, 2014/05/23 13:33:17]

InstallOnDevice has @decorators.Cache. So the subsequent calls are free.

     self._powermonitor_process_port = int(
         self._device.old_interface.RunShellCommand(
             '%s %d %s %s %s' % (self._file_poller_binary, SAMPLE_RATE_HZ,