about:tracing: tweak next/prev nagivation
about:tracing: tweak next/prev nagivation

When using next/prev to step through a selection:
1. don't clear the selection when walking off the end
2. move the viewport to keep the left/right edge visible

BUG=none
TEST=zoom in; select a block of events (or one); use left/right arrow keys to navigate and watch the selection area and the display

Change-Id: If1667240996719ceb0c0143fd61ecea93a94e4f8


Review URL: http://codereview.chromium.org/10007018

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@131825 0039d316-1c4b-4281-b951-d872f2087c98

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