Ship headers from ui/shell_dialogs.
Should import subprocess module before using it.

The traceback:
Traceback (most recent call last):
  File "./script/create-dist", line 174, in <module>
    sys.exit(main())
  File "./script/create-dist", line 63, in main
    create_dsym()
  File "./script/create-dist", line 92, in create_dsym
    subprocess.check_call(['dsymutil', source, '-o', destination_dsym])
NameError: global name 'subprocess' is not defined
Merge pull request #6 from aroben/shell_dialogs

Ship headers from ui/shell_dialogs