Add -Wsign-compare for C++ compilation on linux & friends. g++ -Wall includes -Wsign-compare on C++ source, but clang++ doesn't.
Add -Wsign-compare for C++ compilation on linux & friends.
g++ -Wall includes -Wsign-compare on C++ source, but clang++ doesn't.

(this is a 2nd attempt to land this change, after 79846 had to be rolled back
because clang's -Wsign-compare semantics were different from gcc's; this has
been fixed in clang 135664)

BUG=none
TEST=chrome builds w/ rolled clang, trybots

Review URL: http://codereview.chromium.org/7493029

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@93837 0039d316-1c4b-4281-b951-d872f2087c98

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