Extract the shell runner into devtools.

mojo/devtools/common/mojo_shell

Index: mojo/devtools/common/mojo_shell
diff --git a/mojo/tools/mojo_shell.py b/mojo/devtools/common/mojo_shell
similarity index 85%
copy from mojo/tools/mojo_shell.py
copy to mojo/devtools/common/mojo_shell
index 4c303d9ed04cc32bc6a6cabc8ff7f131eb42bd7d..517b38e95d0abe2f2156fcd64499b58d062db394 100755
--- a/mojo/tools/mojo_shell.py
+++ b/mojo/devtools/common/mojo_shell
@@ -6,19 +6,13 @@
 import argparse
 import logging
 import sys
-import os.path
-import subprocess
 
-import devtools
-devtools.add_lib_to_path()
 from devtoolslib.android_shell import AndroidShell
 from devtoolslib.linux_shell import LinuxShell
 from devtoolslib import shell_arguments
+from devtoolslib import default_paths
 
-from mopy.config import Config
-from mopy.paths import Paths
-
-USAGE = ("mojo_shell.py "
+USAGE = ("mojo_shell "
          "[--args-for=<mojo-app>] "
          "[--content-handlers=<handlers>] "
          "[--enable-external-applications] "
@@ -81,31 +75,30 @@ def main():
                       '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
+
   if launcher_args.android:
-    config = Config(target_os=Config.OS_ANDROID,
-                    target_cpu=launcher_args.target_cpu,
-                    is_debug=launcher_args.debug)
-    paths = Paths(config)
     verbose_pipe = sys.stdout if launcher_args.verbose else None
 
-    shell = AndroidShell(paths.adb_path, launcher_args.target_device,
+    shell = AndroidShell(paths['adb'], 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.target_mojo_shell_path)
+    shell.InstallApk(paths['shell'])
 
     args = shell_arguments.RewriteMapOriginParameters(shell, args)
     if not launcher_args.origin:
-      args.extend(shell_arguments.ConfigureLocalOrigin(shell, paths.build_dir))
+      args.extend(shell_arguments.ConfigureLocalOrigin(shell, paths['build']))
   else:
-    config = Config(target_os=Config.OS_LINUX,
-                    target_cpu=launcher_args.target_cpu,
-                    is_debug=launcher_args.debug)
-    paths = Paths(config)
-    shell = LinuxShell(paths.mojo_shell_path)
+    shell = LinuxShell(paths['shell'])
     if launcher_args.use_osmesa:
       args.append('--args-for=mojo:native_viewport_service --use-osmesa')
 
@@ -122,12 +115,10 @@ def main():
     # are accessible using a root-relative path) and Sky packages at /packages.
     # This is independent from the server that potentially serves the origin
     # directory containing the mojo: apps.
-    packages_local_path = os.path.join(paths.build_dir, 'gen', 'dart-pkg',
-                                       'packages')
     additional_mappings = [
-        ('packages/', packages_local_path),
+        ('packages/', paths['sky_packages']),
     ]
-    server_url = shell.ServeLocalDirectory(paths.src_root,
+    server_url = shell.ServeLocalDirectory(paths['root'],
         port=_SKY_SERVER_PORT, additional_mappings=additional_mappings)
 
     # Configure the content type mappings for the sky_viewer. This is needed