fix excesive number of mutexes created by sandbox

fix excesive number of mutexes created by sandbox

The |cient_control->server_alive| mutex was being created for each
target (child) process and leaked (that part is necessary). Instead
a single mutex can be reused for all targets.

R=rvargas
BUG=331241
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=252782

[cpu_(ooo_6.6-7.5), 2014-02-20 02:44:19]

I used the old style to be consistent with the surrounding code and other parts
of the sandbox.

[rvargas (doing something else), 2014-02-20 15:45:53]

lgtm

https://codereview.chromium.org/167593003/diff/1/sandbox/win/src/sharedmem_ip...
File sandbox/win/src/sharedmem_ipc_server.cc (right):

https://codereview.chromium.org/167593003/diff/1/sandbox/win/src/sharedmem_ip...
sandbox/win/src/sharedmem_ipc_server.cc:16: // This handle must not be closed.
nit: add a line here or remove line 18

https://codereview.chromium.org/167593003/diff/1/sandbox/win/src/sharedmem_ip...
sandbox/win/src/sharedmem_ipc_server.cc:131: g_alive_mutex,
nit: move to the previous line.

[cpu_(ooo_6.6-7.5), 2014-02-22 00:33:14]

The CQ bit was checked by cpu@chromium.org

[commit-bot: I haz the power, 2014-02-22 00:36:42]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/cpu@chromium.org/167593003/90001

[commit-bot: I haz the power, 2014-02-22 01:33:37]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/cpu@chromium.org/167593003/90001

[commit-bot: I haz the power, 2014-02-22 08:31:37]

Change committed as 252782