Implement scrolling in Pepper. This does simple scrolling of the backing store in the renderer, and just invalidates that region so it's repainted by WebKit.
Implement scrolling in Pepper. This does simple scrolling of the backing store
in the renderer, and just invalidates that region so it's repainted by WebKit.

TEST=covered by ppapi unit test (to be enabled)
BUG=none
Review URL: http://codereview.chromium.org/2909017

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@52444 0039d316-1c4b-4281-b951-d872f2087c98

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