Make the serialization of IPC::Messages inside other IPC::Messages independent

Make the serialization of IPC::Messages inside other IPC::Messages independent
of the platform.

This is necessary for sending nested messages between nacl (which the IPC
system thinks is posix and so has extra header goo) and a Windows client app
(which doesn't have this stuff).

BUG=

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=144840

[darin (slow to review), 2012-06-22 21:42:16]

LGTM

https://chromiumcodereview.appspot.com/10667002/diff/1/ipc/ipc_message.h
File ipc/ipc_message.h (right):

https://chromiumcodereview.appspot.com/10667002/diff/1/ipc/ipc_message.h#newc...
ipc/ipc_message.h:156: // This is used when deserializing nested messages. It
sets the given header
nit: people often fail to update comments like this when they start using a
function for more than one purpose.  maybe leave off the comment about where the
function is used?  easy to grep for...

[commit-bot: I haz the power, 2012-06-22 22:36:26]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/brettw@chromium.org/10667002/5001

[commit-bot: I haz the power, 2012-06-22 23:23:09]

Try job failure for 10667002-5001 (retry) on win for step "compile" (clobber
build).
It's a second try, previously, step "compile" failed.
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=win&number...

[commit-bot: I haz the power, 2012-06-28 19:56:01]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/brettw@chromium.org/10667002/7004

[commit-bot: I haz the power, 2012-06-28 22:20:17]

Try job failure for 10667002-7004 (retry) on win_rel for step "browser_tests".
It's a second try, previously, step "browser_tests" failed.
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=win_rel&nu...