Increase maximum file descriptors per IPC message on POSIX from 5 to 7

Increase maximum file descriptors per IPC message on POSIX from 5 to 7.

On POSIX, the maximum number of file descriptors passable in an IPC message is controlled by a constant 'kMaxDescriptorsPerMessage'. It's currently set at 5. This patch makes it 7.

The Picasa album table reader utility process (https://codereview.chromium.org/18986012/) needs to pass 7 files to the utility process. This works on Windows, but fails on POSIX (Mac), due to the aforementioned limit. This CL increases this limit to 7, as well as adds some DLOG messages to give better info to developers who hit this limit.

ipc_channel_posix.cc seems to indicate adding extra file descriptors just makes the messages longer by an 'int' per file descriptor. Making the maximum even larger would be okay with me too.

BUG=

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=220371

[tommycli, 2013-08-29 01:16:57]

jam: Need OWNER review for ipc/.

[jam, 2013-08-29 05:04:44]

please send this to an IPC owner that's more familiar with posix

[tommycli, 2013-08-29 17:18:44]

agl: Need OWNER review

[tommycli, 2013-08-29 17:20:19]

FYI: Last time it was increased was 2011:
http://codereview.chromium.org/7010015

[agl, 2013-08-29 17:22:34]

LGTM.

The limit of 5 was set to be "crazy high". I shudder to think what kind of IPC
message needs 7, but I assume that there's a good reason.

[tommycli, 2013-08-29 17:38:03]

On 2013/08/29 17:22:34, agl wrote:
> LGTM.
> 
> The limit of 5 was set to be "crazy high". I shudder to think what kind of IPC
> message needs 7, but I assume that there's a good reason.

Thanks!

Is it really that crazy to open 7 files and need them to be processed by a
utility process?

[commit-bot: I haz the power, 2013-08-29 17:38:48]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/tommycli@chromium.org/23534018/1

[commit-bot: I haz the power, 2013-08-29 21:15:47]

Change committed as 220371