Fixes for re-enabling more MSVC level 4 warnings: content/ edition

Fixes for re-enabling more MSVC level 4 warnings: content/ edition

This contains fixes for the following sorts of issues:
* Signedness mismatch
* Possibly-uninitialized local variable
* Assignment inside conditional
* Nonstandard extension: unnamed struct/union

This also contains a very small number of other cleanups/simplifications to
nearby code.

BUG=81439
TEST=none

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=283161

[Peter Kasting, 2014-07-11 17:22:25]

Friendly ping

[Peter Kasting, 2014-07-14 20:49:42]

Brett, can you review this?  John seems to be unresponsive (maybe away).

[brettw, 2014-07-14 21:08:28]

lgtm

[Peter Kasting, 2014-07-14 21:09:27]

The CQ bit was checked by pkasting@chromium.org

[commit-bot: I haz the power, 2014-07-14 21:10:36]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/pkasting@chromium.org/377723002/1

[commit-bot: I haz the power, 2014-07-14 23:57:18]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  chromium_presubmit on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/chromium_presubmit/bu...)

[Peter Kasting, 2014-07-14 23:59:47]

+cpu for sandbox_win.cc

[cpu_(ooo_6.6-7.5), 2014-07-15 00:26:07]

lgtm

[commit-bot: I haz the power, 2014-07-15 06:50:43]

Change committed as 283161