[devil] Add as_root option to DeviceUtils.PathExists.

devil/devil/android/device_utils.py

Index: devil/devil/android/device_utils.py
diff --git a/devil/devil/android/device_utils.py b/devil/devil/android/device_utils.py
index 05f3181b494d2fbcd47e2e48ae7619b7961dc3e2..bd556ba3d69d6df241b155810d53ce84cdae326c 100644
--- a/devil/devil/android/device_utils.py
+++ b/devil/devil/android/device_utils.py
@@ -1367,12 +1367,14 @@ class DeviceUtils(object):
     """
     return self.PathExists(device_path, timeout=timeout, retries=retries)
 
-  def PathExists(self, device_paths, timeout=None, retries=None):
+  def PathExists(self, device_paths, as_root=False, timeout=None, retries=None):
     """Checks whether the given path(s) exists on the device.
 
     Args:
       device_path: A string containing the absolute path to the file on the
                    device, or an iterable of paths to check.
+      as_root: Whether root permissions should be use to check for the existence
+               of the given path(s).
       timeout: timeout in seconds
       retries: number of retries
 
@@ -1387,10 +1389,13 @@ class DeviceUtils(object):
     if isinstance(paths, basestring):
       paths = (paths,)
     condition = ' -a '.join('-e %s' % cmd_helper.SingleQuote(p) for p in paths)
-    cmd = 'test %s;echo $?' % condition
-    result = self.RunShellCommand(cmd, check_return=True, timeout=timeout,
-                                  retries=retries)
-    return '0' == result[0]
+    cmd = 'test %s' % condition
+    try:
+      self.RunShellCommand(cmd, as_root=as_root, check_return=True,
+                           timeout=timeout, retries=retries)
+      return True
+    except device_errors.CommandFailedError:
+      return False
 
   @decorators.WithTimeoutAndRetriesFromInstance()
   def PullFile(self, device_path, host_path, timeout=None, retries=None):