Print a nicer error if installing an APK fails when you have not run adb root.

build/android/gyp/apk_install.py

 #!/usr/bin/env python
 #
 # Copyright 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """Installs an APK.
 
 """
 
@@ skipping 31 matching lines @@
     return True
 
   with open(metadata_path, 'r') as expected_file:
     return expected_file.read() != GetMetadata(apk_package)
 
 
 def RecordInstallMetadata(apk_package, metadata_path):
   """Records the metadata from the device for apk_package."""
   metadata = GetMetadata(apk_package)
   if not metadata:
-    raise 'APK install failed unexpectedly.'
+    if not android_commands.AndroidCommands().IsRootEnabled():
+      raise Exception('APK install failed unexpectedly -- root not enabled on '
+                      'the device (run adb root).')
+    raise Exception('APK install failed unexpectedly.')
 
   with open(metadata_path, 'w') as outfile:
     outfile.write(metadata)
 
 
 def main(argv):
   if not build_utils.IsDeviceReady():
     build_utils.PrintBigWarning(
         'Zero (or multiple) devices attached. Skipping APK install.')
     return
@@ skipping 37 matching lines @@
       input_paths=[options.apk_path],
       input_strings=install_cmd,
       force=force_install)
 
   if options.stamp:
     build_utils.Touch(options.stamp)
 
 
 if __name__ == '__main__':
   sys.exit(main(sys.argv))