Fix force stop using wrong "ps" cmd.

devil/devil/android/device_utils_test.py

Index: devil/devil/android/device_utils_test.py
diff --git a/devil/devil/android/device_utils_test.py b/devil/devil/android/device_utils_test.py
index 2490209631075502df03c9f81c035b8da05ef2b6..975399e3ab69a6fec73b6405f7306a247e868528 100755
--- a/devil/devil/android/device_utils_test.py
+++ b/devil/devil/android/device_utils_test.py
@@ -1539,10 +1539,17 @@ class DeviceUtilsGoHomeTest(DeviceUtilsTest):
 class DeviceUtilsForceStopTest(DeviceUtilsTest):
 
   def testForceStop(self):
+    with self.assertCalls(
+        (self.call.device.GetPids('test.package'), {'test.package': [1111]}),
+        (self.call.device.RunShellCommand(
+            ['am', 'force-stop', 'test.package'],
+            check_return=True),
+         ['Success'])):
+      self.device.ForceStop('test.package')
+
+  def testForceStop_NoProcessFound(self):
     with self.assertCall(
-        self.call.adb.Shell('p=test.package;if [[ "$(ps)" = *$p* ]]; then '
-                            'am force-stop $p; fi'),
-        ''):
+        self.call.device.GetPids('test.package'), {}):
       self.device.ForceStop('test.package')