[Telemetry] Assert that android devices are rooted when running telemetry.

telemetry/telemetry/internal/platform/android_platform_backend.py

Index: telemetry/telemetry/internal/platform/android_platform_backend.py
diff --git a/telemetry/telemetry/internal/platform/android_platform_backend.py b/telemetry/telemetry/internal/platform/android_platform_backend.py
index 2f0def7dae8839171ab50746e69fc37ade437282..34e44854a84c3f49dc52bb3ece97e13aaff18118 100644
--- a/telemetry/telemetry/internal/platform/android_platform_backend.py
+++ b/telemetry/telemetry/internal/platform/android_platform_backend.py
@@ -78,6 +78,8 @@ class AndroidPlatformBackend(
         self._device.EnableRoot()
       except device_errors.CommandFailedError:
         logging.warning('Unable to root %s', str(self._device))
+    assert self._device.HasRoot(), (
+        'Android device must be rooted to run Telemetry')
     self._battery = battery_utils.BatteryUtils(self._device)
     self._enable_performance_mode = device.enable_performance_mode
     self._surface_stats_collector = None