Change common_message_generator code block.

Change common_message_generator code block.

Makes namespace IPC {} more tightly wrapped around the inclusion of
the genertor header file.

Updates comments in ipc_message_macros to indicate this new style of block.
Makes message ID generation into a macro so can be re-used in forthcoming
ipclist CL. Simplfies the NULL macros.

Adds #pragma once to param traits, because we can.


Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=77943

[Tom Sepez, 2011-03-11 23:02:04]

First part of ipclist CL -- parts of message generator code blocks that need to
be tightened, and tidy up ipc a bit.

[jam, 2011-03-11 23:19:53]

lgtm

http://codereview.chromium.org/6683014/diff/1/ipc/ipc_message_macros.h
File ipc/ipc_message_macros.h (right):

http://codereview.chromium.org/6683014/diff/1/ipc/ipc_message_macros.h#newcode38
ipc/ipc_message_macros.h:38: // the following code:
nit: it might be easier for people to copy it if C style comments were used
here.