Fix tautological compares in font_atlas.cc.

Fix tautological compares in font_atlas.cc.

This fixes the following warnings from a recent version of Clang:

cc/font_atlas.cc:62:43: error: comparison of constant 128 with
expression of type 'char' is always true
[-Werror,-Wtautological-constant-out-of-range-compare]

cc/font_atlas.cc:45:39: error: comparison of constant 128 with
expression of type 'const char' is always true
[-Werror,-Wtautological-constant-out-of-range-compare]

The problem is that the char type is signed on this platform, and
therefore always < 128. The code really wants to work with the unsigned
values here.

BUG=163104
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=170041

[jamesr, 2012-11-28 17:48:44]

lgtm

[commit-bot: I haz the power, 2012-11-28 18:00:41]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/hans@chromium.org/11416239/1

[commit-bot: I haz the power, 2012-11-28 20:33:02]

Change committed as 170041