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


Review URL: https://chromiumcodereview.appspot.com/11416239

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@170041 0039d316-1c4b-4281-b951-d872f2087c98

dushu1203/chromium.src,krieger-od/nwjs_chromium.src,ondra-novak/chromium.src,fujunwei/chromium-crosswalk,fujunwei/chromium-crosswalk,bright-sparks/chromium-spacewalk,ChromiumWebApps/chromium,krieger-od/nwjs_chromium.src,pozdnyakov/chromium-crosswalk,Pluto-tv/chromium-crosswalk,PeterWangIntel/chromium-crosswalk,timopulkkinen/BubbleFish,Fireblend/chromium-crosswalk,nacl-webkit/chrome_deps,chuan9/chromium-crosswalk,hujiajie/pa-chromium,patrickm/chromium.src,Fireblend/chromium-crosswalk,chuan9/chromium-crosswalk,ondra-novak/chromium.src,dednal/chromium.src,anirudhSK/chromium,hgl888/chromium-crosswalk-efl,fujunwei/chromium-crosswalk,crosswalk-project/chromium-crosswalk-efl,dushu1203/chromium.src,nacl-webkit/chrome_deps,dushu1203/chromium.src,crosswalk-project/chromium-crosswalk-efl,Jonekee/chromium.src,littlstar/chromium.src,hujiajie/pa-chromium,bright-sparks/chromium-spacewalk,hujiajie/pa-chromium,ltilve/chromium,chuan9/chromium-crosswalk,dushu1203/chromium.src,hujiajie/pa-chromium,Just-D/chromium-1,axinging/chromium-crosswalk,mogoweb/chromium-crosswalk,pozdnyakov/chromium-crosswalk,Jonekee/chromium.src,anirudhSK/chromium,zcbenz/cefode-chromium,jaruba/chromium.src,fujunwei/chromium-crosswalk,crosswalk-project/chromium-crosswalk-efl,jaruba/chromium.src,Jonekee/chromium.src,patrickm/chromium.src,Jonekee/chromium.src,dednal/chromium.src,mogoweb/chromium-crosswalk,axinging/chromium-crosswalk,timopulkkinen/BubbleFish,TheTypoMaster/chromium-crosswalk,Jonekee/chromium.src,hgl888/chromium-crosswalk-efl,patrickm/chromium.src,nacl-webkit/chrome_deps,PeterWangIntel/chromium-crosswalk,Jonekee/chromium.src,Just-D/chromium-1,hgl888/chromium-crosswalk-efl,bright-sparks/chromium-spacewalk,ChromiumWebApps/chromium,M4sse/chromium.src,ChromiumWebApps/chromium,crosswalk-project/chromium-crosswalk-efl,bright-sparks/chromium-spacewalk,anirudhSK/chromium,Jonekee/chromium.src,PeterWangIntel/chromium-crosswalk,dednal/chromium.src,Chilledheart/chromium,M4sse/chromium.src,Pluto-tv/chromium-crosswalk,ChromiumWebApps/chromium,Pluto-tv/chromium-crosswalk,zcbenz/cefode-chromium,Fireblend/chromium-crosswalk,pozdnyakov/chromium-crosswalk,ChromiumWebApps/chromium,dushu1203/chromium.src,Fireblend/chromium-crosswalk,timopulkkinen/BubbleFish,krieger-od/nwjs_chromium.src,dednal/chromium.src,timopulkkinen/BubbleFish,Chilledheart/chromium,TheTypoMaster/chromium-crosswalk,anirudhSK/chromium,hgl888/chromium-crosswalk,dushu1203/chromium.src,pozdnyakov/chromium-crosswalk,nacl-webkit/chrome_deps,krieger-od/nwjs_chromium.src,pozdnyakov/chromium-crosswalk,TheTypoMaster/chromium-crosswalk,crosswalk-project/chromium-crosswalk-efl,zcbenz/cefode-chromium,markYoungH/chromium.src,Chilledheart/chromium,Fireblend/chromium-crosswalk,ondra-novak/chromium.src,nacl-webkit/chrome_deps,anirudhSK/chromium,pozdnyakov/chromium-crosswalk,hgl888/chromium-crosswalk,hgl888/chromium-crosswalk,ondra-novak/chromium.src,nacl-webkit/chrome_deps,krieger-od/nwjs_chromium.src,patrickm/chromium.src,patrickm/chromium.src,Chilledheart/chromium,M4sse/chromium.src,anirudhSK/chromium,ltilve/chromium,littlstar/chromium.src,dushu1203/chromium.src,chuan9/chromium-crosswalk,bright-sparks/chromium-spacewalk,fujunwei/chromium-crosswalk,markYoungH/chromium.src,hgl888/chromium-crosswalk,crosswalk-project/chromium-crosswalk-efl,ChromiumWebApps/chromium,littlstar/chromium.src,mohamed--abdel-maksoud/chromium.src,krieger-od/nwjs_chromium.src,mogoweb/chromium-crosswalk,ltilve/chromium,M4sse/chromium.src,Just-D/chromium-1,crosswalk-project/chromium-crosswalk-efl,jaruba/chromium.src,Pluto-tv/chromium-crosswalk,hgl888/chromium-crosswalk-efl,hujiajie/pa-chromium,TheTypoMaster/chromium-crosswalk,littlstar/chromium.src,axinging/chromium-crosswalk,chuan9/chromium-crosswalk,Jonekee/chromium.src,TheTypoMaster/chromium-crosswalk,markYoungH/chromium.src,Just-D/chromium-1,bright-sparks/chromium-spacewalk,M4sse/chromium.src,Chilledheart/chromium,jaruba/chromium.src,Just-D/chromium-1,anirudhSK/chromium,TheTypoMaster/chromium-crosswalk,Jonekee/chromium.src,ltilve/chromium,littlstar/chromium.src,axinging/chromium-crosswalk,Fireblend/chromium-crosswalk,dednal/chromium.src,mohamed--abdel-maksoud/chromium.src,crosswalk-project/chromium-crosswalk-efl,ChromiumWebApps/chromium,markYoungH/chromium.src,markYoungH/chromium.src,hujiajie/pa-chromium,zcbenz/cefode-chromium,ltilve/chromium,zcbenz/cefode-chromium,jaruba/chromium.src,krieger-od/nwjs_chromium.src,hgl888/chromium-crosswalk,mogoweb/chromium-crosswalk,jaruba/chromium.src,anirudhSK/chromium,timopulkkinen/BubbleFish,dednal/chromium.src,mohamed--abdel-maksoud/chromium.src,Fireblend/chromium-crosswalk,zcbenz/cefode-chromium,littlstar/chromium.src,dushu1203/chromium.src,littlstar/chromium.src,ondra-novak/chromium.src,PeterWangIntel/chromium-crosswalk,PeterWangIntel/chromium-crosswalk,mohamed--abdel-maksoud/chromium.src,chuan9/chromium-crosswalk,ChromiumWebApps/chromium,chuan9/chromium-crosswalk,axinging/chromium-crosswalk,ChromiumWebApps/chromium,markYoungH/chromium.src,M4sse/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