Make the shell work in multiprocess mode some apps.

Make the shell work in multiprocess mode some apps.

$ out/Debug/mojo_shell mojo:wget --enable-multiprocess \
    --args-for="mojo:wget http://www.google.com/"

works.

Modifying wget to not quit, I can do:

$ ps -ef | grep mojo_shell
vtl      12159  9625  0 13:40 pts/13   00:00:00 out/Debug/mojo_shell mojo:wget --enable-multiprocess --args-for=mojo:wget http://www.google.com/
vtl      12163 12159  0 13:40 pts/13   00:00:00 out/Debug/mojo_shell --child-process-type=1 --mojo-platform-channel-handle=3
vtl      12164 12159  0 13:40 pts/13   00:00:00 out/Debug/mojo_shell --child-process-type=1 --mojo-platform-channel-handle=3
vtl      12169 12159  0 13:40 pts/13   00:00:00 out/Debug/mojo_shell --child-process-type=1 --mojo-platform-channel-handle=3

Notes:
* It doesn't work without the "--args-for", since then wget would try to
  read the URL from stdin (and fail) and pass on an empty URL.
* wget and its process actually shut down cleanly.
* However, the end of the last "interactive" app leads the shell to
  terminate with extreme prejudice, just cutting off the feet of the
  other processes. This is why we get messages like:
    [WARNING:child_process_host.cc(35)] Destroying ChildProcessHost with unjoined child
    [ERROR:app_child_process.cc(208)] Connection error to the shell.
* spinning_cube doesn't work yet, since we'll need to specially load
  some apps in-process.
* I made the command-line argument checking only apply to the main
  process (i.e., when --child-process-type is NOT present). Otherwise,
  I'd have to plumb through another flag (from platform_channel_pair.*)
  and not choke when there are no positional command-line arguments.

R=jamesr@chromium.org

Committed: https://chromium.googlesource.com/external/mojo/+/f3e4e33c1983dc8cf74375285b0608eb5d931b71

[jamesr, 2015-03-03 21:56:24]

lgtm

https://codereview.chromium.org/973203004/diff/1/shell/switches.cc
File shell/switches.cc (right):

https://codereview.chromium.org/973203004/diff/1/shell/switches.cc#newcode65
shell/switches.cc:65: // |kChildProcessType| not for user use.
if it's not for user use who can use it?

(why not just delete this?)

[viettrungluu, 2015-03-03 22:07:17]

Thanks.

On 2015/03/03 21:56:24, jamesr wrote:
> lgtm
> 
> https://codereview.chromium.org/973203004/diff/1/shell/switches.cc
> File shell/switches.cc (right):
> 
> https://codereview.chromium.org/973203004/diff/1/shell/switches.cc#newcode65
> shell/switches.cc:65: // |kChildProcessType| not for user use.
> if it's not for user use who can use it?
> 
> (why not just delete this?)

It's for the main process to pass to the child process. I'll clarify in the
comment for kChildProcessType.

[viettrungluu, 2015-03-03 22:11:20]

Committed patchset #2 (id:20001) manually as
f3e4e33c1983dc8cf74375285b0608eb5d931b71 (presubmit successful).