Try to enable root when starting adb, as root is needed for a full coverage.

tools/telemetry/telemetry/core/backends/chrome/android_browser_finder.py

Index: tools/telemetry/telemetry/core/backends/chrome/android_browser_finder.py
diff --git a/tools/telemetry/telemetry/core/backends/chrome/android_browser_finder.py b/tools/telemetry/telemetry/core/backends/chrome/android_browser_finder.py
index 846e47d8d667b712b6ecbd267e3c1c48f6b6d3a6..2fa9fd0ad2e6bd2d9fe08246dd26fa1fb6b73cde 100644
--- a/tools/telemetry/telemetry/core/backends/chrome/android_browser_finder.py
+++ b/tools/telemetry/telemetry/core/backends/chrome/android_browser_finder.py
@@ -199,6 +199,10 @@ def FindAllAvailableBrowsers(finder_options, logging=real_logging):
   device = devices[0]
 
   adb = adb_commands.AdbCommands(device=device)
+  # Trying to root the device, if possible.
+  if not adb.IsRootEnabled():

[tonyg, 2014/05/20 11:53:38]

Is this check even necessary? I think the below will just be a no-op if it
already has root, right?

[qsr, 2014/05/20 11:58:31]

 Yes, but it does a few SendCommand, and maybe a shell restart, so cutting that
seemed a good idea. If you prefer I remove it, I can.

+    # Ignore result.
+    adb.EnableAdbRoot()
 
   if sys.platform.startswith('linux'):
     # Host side workaround for crbug.com/268450 (adb instability)