Revert of Refactor perf bisect script _CalculateConfidence method. (https://codereview.chromium.org/209853009/)
Revert of Refactor perf bisect script _CalculateConfidence method. (https://codereview.chromium.org/209853009/)

Reason for revert:
Caused issue 358622.

The bug was that at line 2832 I used a tuple instead of a list, then later I tried to assign to a member of the tuple, but Python tuples are immutable.

Original issue's description:
> Refactor perf bisect script _CalculateConfidence method.
> 
>  - Adding docstrings
>  - Factoring out _CalculateBounds method
>  - Bug fix???
> 
> BUG=
> 
> Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=260241

TBR=prasadv@chromium.org,simonhatch@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=

Review URL: https://codereview.chromium.org/218613012

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@260885 0039d316-1c4b-4281-b951-d872f2087c98

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