Add input latency UMA stats in impl thread      Currently RenderWidget tracks input event latency through UMA stats Event.Latency.Renderer.XXX. But not all events sent to renderer get to main thread (where RenderWidget lives), e.g. GestureScrollXXX will be handled in Impl thread for fast path scroll.      This CL adds a new UMA stats "Event.Latency.RendererImpl.GestureScroll" to track the latency from the time the scroll event is originally created (On Aura, this is the OS timestamp of the initial touch event) to the time the GestureScroll reaches renderer impl thread.      BUG=243443 TEST=1. On Pixel, go to page en.wikipedia.org/wiki/Cat and scroll the page 2. Check there IS NO chrome://histogram/Event.Latency.Renderer.GestureScrollUpdate 3. Check there IS chrome://histogram/Event.Latency.RendererImpl.GestureScroll
Add input latency UMA stats in impl thread
    
Currently RenderWidget tracks input event latency through UMA stats
Event.Latency.Renderer.XXX. But not all events sent to renderer get
to main thread (where RenderWidget lives), e.g. GestureScrollXXX will
be handled in Impl thread for fast path scroll.
    
This CL adds a new UMA stats "Event.Latency.RendererImpl.GestureScroll"
to track the latency from the time the scroll event is originally created
(On Aura, this is the OS timestamp of the initial touch event) to the time
the GestureScroll reaches renderer impl thread.
    
BUG=243443
TEST=1. On Pixel, go to page en.wikipedia.org/wiki/Cat and scroll the page
2. Check there IS NO chrome://histogram/Event.Latency.Renderer.GestureScrollUpdate
3. Check there IS chrome://histogram/Event.Latency.RendererImpl.GestureScroll

Review URL: https://chromiumcodereview.appspot.com/16153010

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@208634 0039d316-1c4b-4281-b951-d872f2087c98

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