Support startup performance tests on Galaxy S3

build/android/pylib/perf_tests_helper.py

Index: build/android/pylib/perf_tests_helper.py
diff --git a/build/android/pylib/perf_tests_helper.py b/build/android/pylib/perf_tests_helper.py
index ee2519bbd3a2b523a57700d26019184c5c478449..68e4c943aae74e125b29b8fe1b683503a882edd7 100644
--- a/build/android/pylib/perf_tests_helper.py
+++ b/build/android/pylib/perf_tests_helper.py
@@ -142,10 +142,8 @@ class PerfTestSetup(object):
 
   def DropRamCaches(self):
     """Drops the filesystem ram caches for performance testing."""
-    if not self._adb.IsRootEnabled():
-      self._adb.EnableAdbRoot()
-    self._adb.RunShellCommand('sync')
-    self._adb.RunShellCommand('echo 3 > ' + PerfTestSetup._DROP_CACHES)
+    self._adb.RunShellCommand('su -c sync')
+    self._adb.SetProtectedFileContents(PerfTestSetup._DROP_CACHES, '3')
 
   def SetUp(self):
     """Sets up performance tests."""
@@ -165,6 +163,5 @@ class PerfTestSetup(object):
   def _SetScalingGovernorInternal(self, value):
     for cpu in range(self._kernel_max + 1):
       scaling_governor_file = PerfTestSetup._SCALING_GOVERNOR_FMT % cpu
-      if self._adb.Adb().DoesFileExist(scaling_governor_file):
-        self._adb.RunShellCommand(
-            ('echo %s > ' + scaling_governor_file) % value)
+      if self._adb.FileExistsOnDevice(scaling_governor_file):
+        self._adb.SetProtectedFileContents(scaling_governor_file, value)