Revert of Simplify mojo_shell since it's now only used for Mandoline.

mojo/tools/android_mojo_shell.py

Index: mojo/tools/android_mojo_shell.py
diff --git a/mojo/tools/android_mojo_shell.py b/mojo/tools/android_mojo_shell.py
index e2692282917cbe588e17a2a32127f4ef9c536004..d731afe9ef7b41a7521e3bb8ca7901879d586484 100755
--- a/mojo/tools/android_mojo_shell.py
+++ b/mojo/tools/android_mojo_shell.py
@@ -10,10 +10,28 @@ import sys
 from mopy.config import Config
 from mopy import android
 
+USAGE = ("android_mojo_shell.py "
+         "[--args-for=<mojo-app>] "
+         "[--content-handlers=<handlers>] "
+         "[--enable-external-applications] "
+         "[--disable-cache] "
+         "[--enable-multiprocess] "
+         "[--url-mappings=from1=to1,from2=to2] "
+         "[<mojo-app>] "
+         """
+
+A <mojo-app> is a Mojo URL or a Mojo URL and arguments within quotes.
+Example: mojo_shell "mojo:js_standalone test.js".
+<url-lib-path> is searched for shared libraries named by mojo URLs.
+The value of <handlers> is a comma separated list like:
+text/html,mojo:html_viewer,application/javascript,mojo:js_content_handler
+""")
+
+
 def main():
   logging.basicConfig()
 
-  parser = argparse.ArgumentParser("Helper for running mojo_shell")
+  parser = argparse.ArgumentParser(usage=USAGE)
 
   debug_group = parser.add_mutually_exclusive_group()
   debug_group.add_argument('--debug', help='Debug build (default)',