Fixes for re-enabling more MSVC level 4 warnings: base/ edition #2

Fixes for re-enabling more MSVC level 4 warnings: base/ edition #2

This contains fixes for the following sorts of issues:
* Signedness mismatch

Defining UChar32 as a signed type may look wrong, but it's actually how the type
is already defined over in third_party/icu/.

BUG=81439
TEST=none

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=282255

[awong, 2014-07-09 23:15:15]

...scared...LGTM

Eek. Matching makes sense, but that's scary to have the type name express the
wrong signedness.

[awong, 2014-07-09 23:15:50]

Oh...do they mean unicodechar32, not unsinged char32?

[Peter Kasting, 2014-07-09 23:29:22]

On 2014/07/09 23:15:50, awong wrote:
> Oh...do they mean unicodechar32, not unsinged char32?

I didn't think of it until you suggested it, but now that you say it I'm sure
that's what it's supposed to mean.  (That makes me feel better too.)

[Peter Kasting, 2014-07-09 23:29:27]

The CQ bit was checked by pkasting@chromium.org

[commit-bot: I haz the power, 2014-07-09 23:31:33]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/pkasting@chromium.org/380913003/20001

[commit-bot: I haz the power, 2014-07-10 02:47:41]

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...)

[commit-bot: I haz the power, 2014-07-10 04:38:05]

Change committed as 282255