Remove SCM_CREDENTIALS fallback code from breakpad

Remove SCM_CREDENTIALS fallback code from breakpad

Since r266618, we require SCM_CREDENTIALS to work correctly across PID
namespaces, and refuse to run on kernels where it doesn't.

Reland of r270173.  The original attempt failed to update kControlMsgSize,
which caused failures like this one:

http://build.chromium.org/p/chromium.linux/builders/Linux%20Tests%20%28dbg%29%281%29%2832%29/builds/5169

This is only noticed on 32-bit machines because CMSG_SPACE(sizeof(int))
happens to equal CMSG_SPACE(2*sizeof(int)) on x86-64 due to structure
padding and alignment, but they're different on i386.

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=270367

[mdempsky, 2014-05-14 05:38:41]

As requested, patch set 1 is the original erroneous commit.

[Lei Zhang, 2014-05-14 05:53:25]

lgtm

[commit-bot: I haz the power, 2014-05-14 05:53:58]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/mdempsky@chromium.org/271703012/20001

[commit-bot: I haz the power, 2014-05-14 07:37:35]

FYI, CQ is re-trying this CL (attempt #1).
Please consider checking whether the failures are real,
and report flakes to chrome-troopers@google.com.
The failing builders are:
  ios_dbg_simulator on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/ios_dbg_simulator/bui...)
  ios_rel_device on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/ios_rel_device/builds...)

[commit-bot: I haz the power, 2014-05-14 09:18:36]

Change committed as 270367

[mdempsky, 2014-05-14 17:09:14]

mark: FYI, this is a reland of a previous CLs you reviewed that had to be rolled
back.  (It's already been committed and the base changes are identical to what
you already reviewed, so TBR at your own leisure.)

[Mark Mentovai, 2014-05-14 17:29:49]

LGTM