This was recently reported by a user of web_ui here: https://github.com/dart-lang/web-ui/issues/270

We have an 'args' package that we use in several tools and we have other ways to parse options in the dart vm, dart2js, and other internal tools. It will make everyone happy if we support the same set of features everywhere.

Here is where we are today:

* All 3 systems (vm, dart2js, args) accept arguments of this form:

    --option=value
    --flag

* dart2js and args accept abbreviations:

    -f
    -h

  and they accept passing values to an abbreviation directly after it:

    -ovalue

  (Note that the vm accepts some abbreviations like -h and -v, but they are not documented when the usage is printed.)

* dart2js accepts some flags for windows:

    /h /?

* 'args' accepts passing values after a space:

    --option value (same as --option=value)
    -o value (same as -ovalue in dart2js)

* 'args' accepts collapsing bool flags:

    -fbv (same as -f -b -v)

* dart2js accepts passing options after the normal arguments (args requires that all options are passed upfront)

We probably want the union of all these options, which means:
  * change args to support windows flags (maybe only for help?) and allowing options after the normal arguments
  * change dart2js to allow spaces after options and maybe collapsing bool flags abbreviations
  * improve the documentation of options in the vm and allow spaces after options with values (e.g. package-root).

(I'm not sure what area to use for this issue, I'm cc'ing some who I believe are interested in this issue, please add other relevant people that I missed)