Allow the shell runner to run outside of Mojo checkout.

mojo/devtools/common/mojo_shell

 #!/usr/bin/env python
 # Copyright 2014 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.
 
 import argparse
 import logging
 import sys
 
 from devtoolslib.android_shell import AndroidShell
@@ skipping 56 matching lines @@
   parser.add_argument('--logcat-tags',
                       help='(android-only) Comma-separated list of additional '
                       'logcat tags to display on the console.')
 
   # Desktop-only arguments.
   parser.add_argument('--use-osmesa', action='store_true',
                       help='(linux-only) Configure the native viewport service '
                       'for off-screen rendering.')
 
   launcher_args, args = parser.parse_known_args()
-  paths, error_msg = default_paths.infer_default_paths(launcher_args.android,
-                                                       launcher_args.debug,
-                                                       launcher_args.target_cpu)
-  if not paths:
-    print error_msg
-    return -1
+  mojo_paths, _ = default_paths.infer_default_paths(launcher_args.android,
+                                                    launcher_args.debug,
+                                                    launcher_args.target_cpu)
+  if mojo_paths:
+    adb_path = mojo_paths['adb']
+    shell_binary_path = mojo_paths['shell']
+    local_origin_path = mojo_paths['build']
+    if launcher_args.verbose:
+      print 'Running within a Mojo checkout:'
+      print ' - using the locally built shell at ' + shell_binary_path
+      print ' - using the default origin of ' + local_origin_path
+  else:
+    if launcher_args.android:
+      adb_path = 'adb'
+      shell_binary_path = None
+      local_origin_path = '.'
+      if launcher_args.verbose:
+        print 'Running outside a Mojo checkout:'
+        print ' - using the shell already installed on the device'
+        print ' - using the current working directory as default origin'
+    else:
+      print 'Running outside a Mojo checkout is not supported on Linux yet.'
+      return 1
 
   if launcher_args.android:
     verbose_pipe = sys.stdout if launcher_args.verbose else None
 
-    shell = AndroidShell(paths['adb'], launcher_args.target_device,
+    shell = AndroidShell(adb_path, launcher_args.target_device,
                          logcat_tags=launcher_args.logcat_tags,
                          verbose_pipe=verbose_pipe)
     device_status, error = shell.CheckDevice()
     if not device_status:
       print 'Device check failed: ' + error
       return 1
-    shell.InstallApk(paths['shell'])
+    if shell_binary_path:
+      shell.InstallApk(shell_binary_path)
 
     args = shell_arguments.RewriteMapOriginParameters(shell, args)
     if not launcher_args.origin:
-      args.extend(shell_arguments.ConfigureLocalOrigin(shell, paths['build']))
+      args.extend(shell_arguments.ConfigureLocalOrigin(shell,
+                                                       local_origin_path))
   else:
-    shell = LinuxShell(paths['shell'])
+    shell = LinuxShell(shell_binary_path)
     if launcher_args.use_osmesa:
       args.append('--args-for=mojo:native_viewport_service --use-osmesa')
 
   if launcher_args.origin:
     args.append('--origin=' + launcher_args.origin)
   args = shell_arguments.AppendToArgument(args, '--url-mappings=',
                                           'mojo:window_manager=%s' %
                                           launcher_args.window_manager)
   if not launcher_args.no_debugger:
     args.extend(shell_arguments.ConfigureDebugger(shell))
 
   if launcher_args.sky:
-    args.extend(shell_arguments.ConfigureSky(shell, paths['root'],
-                                             paths['sky_packages'],
+    if not mojo_paths:
+      print 'Running with --sky is not supported outside of the Mojo checkout.'
+      # See https://github.com/domokit/devtools/issues/27.
+      return 1
+    args.extend(shell_arguments.ConfigureSky(shell, mojo_paths['root'],
+                                             mojo_paths['sky_packages'],
                                              launcher_args.sky))
 
   if launcher_args.verbose:
     print "Shell arguments: " + str(args)
 
   shell.Run(args)
   return 0
 
 
 if __name__ == "__main__":
   sys.exit(main())