App list folder icons: Fixed off-by-one error.
App list folder icons: Fixed off-by-one error.

Not actually visible to the user. It is not supposed to regenerate the
icon if the fifth or greater item changed. Due to an off-by-one error,
it would still regenerate the icon if the fifth item changed (which is
unnecessary).

NB: Tests are incoming (which would have caught this error).

Also harden a DCHECK (fixing a similar off-by-one error, and making it
into a CHECK because it would be a security issue if it failed).

BUG=425444

Review URL: https://codereview.chromium.org/681373004

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#302030}

krieger-od/nwjs_chromium.src,dushu1203/chromium.src,ltilve/chromium,fujunwei/chromium-crosswalk,dushu1203/chromium.src,jaruba/chromium.src,M4sse/chromium.src,dednal/chromium.src,dednal/chromium.src,dushu1203/chromium.src,krieger-od/nwjs_chromium.src,hgl888/chromium-crosswalk,dednal/chromium.src,dushu1203/chromium.src,jaruba/chromium.src,Pluto-tv/chromium-crosswalk,Jonekee/chromium.src,mohamed--abdel-maksoud/chromium.src,axinging/chromium-crosswalk,Just-D/chromium-1,ltilve/chromium,Pluto-tv/chromium-crosswalk,markYoungH/chromium.src,ltilve/chromium,M4sse/chromium.src,Fireblend/chromium-crosswalk,Chilledheart/chromium,mohamed--abdel-maksoud/chromium.src,TheTypoMaster/chromium-crosswalk,chuan9/chromium-crosswalk,mohamed--abdel-maksoud/chromium.src,Jonekee/chromium.src,chuan9/chromium-crosswalk,PeterWangIntel/chromium-crosswalk,ltilve/chromium,M4sse/chromium.src,axinging/chromium-crosswalk,axinging/chromium-crosswalk,Jonekee/chromium.src,dushu1203/chromium.src,Fireblend/chromium-crosswalk,dushu1203/chromium.src,dednal/chromium.src,krieger-od/nwjs_chromium.src,dednal/chromium.src,Chilledheart/chromium,dednal/chromium.src,TheTypoMaster/chromium-crosswalk,axinging/chromium-crosswalk,dushu1203/chromium.src,mohamed--abdel-maksoud/chromium.src,M4sse/chromium.src,axinging/chromium-crosswalk,chuan9/chromium-crosswalk,Jonekee/chromium.src,M4sse/chromium.src,Pluto-tv/chromium-crosswalk,fujunwei/chromium-crosswalk,dednal/chromium.src,markYoungH/chromium.src,markYoungH/chromium.src,M4sse/chromium.src,Chilledheart/chromium,Fireblend/chromium-crosswalk,axinging/chromium-crosswalk,Just-D/chromium-1,Fireblend/chromium-crosswalk,dushu1203/chromium.src,Fireblend/chromium-crosswalk,fujunwei/chromium-crosswalk,TheTypoMaster/chromium-crosswalk,Jonekee/chromium.src,Just-D/chromium-1,Fireblend/chromium-crosswalk,markYoungH/chromium.src,PeterWangIntel/chromium-crosswalk,jaruba/chromium.src,TheTypoMaster/chromium-crosswalk,axinging/chromium-crosswalk,jaruba/chromium.src,hgl888/chromium-crosswalk,dushu1203/chromium.src,fujunwei/chromium-crosswalk,fujunwei/chromium-crosswalk,Just-D/chromium-1,Pluto-tv/chromium-crosswalk,Chilledheart/chromium,markYoungH/chromium.src,Pluto-tv/chromium-crosswalk,Pluto-tv/chromium-crosswalk,ltilve/chromium,TheTypoMaster/chromium-crosswalk,jaruba/chromium.src,Pluto-tv/chromium-crosswalk,dushu1203/chromium.src,axinging/chromium-crosswalk,jaruba/chromium.src,jaruba/chromium.src,Chilledheart/chromium,markYoungH/chromium.src,krieger-od/nwjs_chromium.src,Fireblend/chromium-crosswalk,krieger-od/nwjs_chromium.src,M4sse/chromium.src,jaruba/chromium.src,chuan9/chromium-crosswalk,axinging/chromium-crosswalk,M4sse/chromium.src,PeterWangIntel/chromium-crosswalk,M4sse/chromium.src,krieger-od/nwjs_chromium.src,hgl888/chromium-crosswalk,krieger-od/nwjs_chromium.src,M4sse/chromium.src,Pluto-tv/chromium-crosswalk,Just-D/chromium-1,mohamed--abdel-maksoud/chromium.src,hgl888/chromium-crosswalk,chuan9/chromium-crosswalk,mohamed--abdel-maksoud/chromium.src,ltilve/chromium,dednal/chromium.src,Chilledheart/chromium,Chilledheart/chromium,jaruba/chromium.src,Jonekee/chromium.src,hgl888/chromium-crosswalk,TheTypoMaster/chromium-crosswalk,hgl888/chromium-crosswalk,Jonekee/chromium.src,dednal/chromium.src,PeterWangIntel/chromium-crosswalk,TheTypoMaster/chromium-crosswalk,mohamed--abdel-maksoud/chromium.src,Chilledheart/chromium,markYoungH/chromium.src,markYoungH/chromium.src,PeterWangIntel/chromium-crosswalk,PeterWangIntel/chromium-crosswalk,ltilve/chromium,hgl888/chromium-crosswalk,fujunwei/chromium-crosswalk,Chilledheart/chromium,Just-D/chromium-1,dushu1203/chromium.src,Just-D/chromium-1,TheTypoMaster/chromium-crosswalk,Fireblend/chromium-crosswalk,ltilve/chromium,Pluto-tv/chromium-crosswalk,jaruba/chromium.src,Jonekee/chromium.src,mohamed--abdel-maksoud/chromium.src,Fireblend/chromium-crosswalk,dednal/chromium.src,PeterWangIntel/chromium-crosswalk,PeterWangIntel/chromium-crosswalk,chuan9/chromium-crosswalk,mohamed--abdel-maksoud/chromium.src,fujunwei/chromium-crosswalk,chuan9/chromium-crosswalk,M4sse/chromium.src,chuan9/chromium-crosswalk,TheTypoMaster/chromium-crosswalk,krieger-od/nwjs_chromium.src,mohamed--abdel-maksoud/chromium.src,axinging/chromium-crosswalk,hgl888/chromium-crosswalk,dednal/chromium.src,jaruba/chromium.src,PeterWangIntel/chromium-crosswalk,hgl888/chromium-crosswalk,krieger-od/nwjs_chromium.src,markYoungH/chromium.src,markYoungH/chromium.src,Jonekee/chromium.src,krieger-od/nwjs_chromium.src,Just-D/chromium-1,markYoungH/chromium.src,axinging/chromium-crosswalk,fujunwei/chromium-crosswalk,ltilve/chromium,Just-D/chromium-1,fujunwei/chromium-crosswalk,krieger-od/nwjs_chromium.src,chuan9/chromium-crosswalk,Jonekee/chromium.src,mohamed--abdel-maksoud/chromium.src,Jonekee/chromium.src