Fixes for re-enabling more MSVC level 4 warnings: base/third_party/dmg_fp/ edition

Fixes for re-enabling more MSVC level 4 warnings: base/third_party/dmg_fp/ edition

This contains fixes for the following sorts of issues:
* Assignment inside conditional

This updates the relevant .patch and README files, combining these fixes with
the previous set of MSVC warning fixes.  This also removes the now-unused
vs2013-optimization.patch file.

BUG=81439
TEST=none

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=282280

[awong, 2014-07-10 00:16:44]

LGTM

[Peter Kasting, 2014-07-10 00:18:47]

The CQ bit was checked by pkasting@chromium.org

[commit-bot: I haz the power, 2014-07-10 00:20:58]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/pkasting@chromium.org/385503002/1

[commit-bot: I haz the power, 2014-07-10 04:02:36]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  mac_chromium_rel on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/mac_chromium_rel/buil...)
  win_chromium_x64_rel on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/win_chromium_x64_rel/...)

[commit-bot: I haz the power, 2014-07-10 08:04:44]

Change committed as 282280