Move statistical functions in bisect script to their own module.

Move statistical functions to another module.

BUG=

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=286137

[qyearsley, 2014-07-24 23:35:45]

As the CL title indicates, the point is just to move some more functions out
into their own module.

I left the confidence function in the main module for two reasons:
 1. Logically speaking, it's not a general-purpose math
    function. It is specific to the bisect script.
 2. Later I want to change it to depend on a third module
    which provides t-test functionality or such. This third
    module might also depend on the functions in math_utils.

I also renamed the methods:
  CalculateConfidence -> ConfidenceScore
  CalculateX -> X
  (because I thought the "Calculate" was unnecessary.)

[prasadv, 2014-07-28 21:31:17]

lgtm

https://codereview.chromium.org/417013003/diff/60001/tools/auto_bisect/math_u...
File tools/auto_bisect/math_utils.py (right):

https://codereview.chromium.org/417013003/diff/60001/tools/auto_bisect/math_u...
tools/auto_bisect/math_utils.py:106: denominator2 += 1.0 / len(current_set)
Nit: if current_set not empty then evaluate denominator2.

[qyearsley, 2014-07-29 01:10:02]

The CQ bit was checked by qyearsley@chromium.org

[commit-bot: I haz the power, 2014-07-29 01:10:43]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/qyearsley@chromium.org/417013003/80001

[commit-bot: I haz the power, 2014-07-29 09:14:48]

Change committed as 286137