Perf dashboard should have UI to test out anomaly detection strategies

Perf dashboard should have UI to test out anomaly detection strategies
https://bugs.webkit.org/show_bug.cgi?id=143290

Reviewed by Benjamin Poulain.

Added the UI to select anomaly detection strategies. The detected anomalies are highlighted in the graph.

Implemented the Western Electric Rules 1 through 4 in http://en.wikipedia.org/wiki/Western_Electric_rules
as well as Welch's t-test that compares the last five points to the prior twenty points.

The latter is what Mozilla uses (or at least did in the past) to detect performance regressions on their
performance tests although they compare medians instead of means.

All of these strategies don't quite work for us since our data points are too noisy but this is a good start.

* public/v2/app.js:
(App.Pane.updateStatisticsTools): Clone anomaly detection strategies.
(App.Pane._updateMovingAverageAndEnvelope): Highlight anomalies detected by the enabled strategies.
(App.Pane._movingAverageOrEnvelopeStrategyDidChange): Observe changes to anomaly detection strategies.
(App.Pane._computeMovingAverageAndOutliers): Detect anomalies by each strategy and aggregate results.
Only report the first data point when multiple consecutive data points are detected as anomalies.
* public/v2/chart-pane.css: Updated styles.
* public/v2/index.html: Added the pane for selecting anomaly detection strategies.
* public/v2/js/statistics.js:
(Statistics.testWelchsT): Added. Implements Welch's t-test.
(.sampleMeanAndVarianceForValues): Added.
(.createWesternElectricRule): Added.
(.countValuesOnSameSide): Added.
(Statistics.AnomalyDetectionStrategy): Added.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@182302 268f45cc-cd09-0410-ab3c-d52691b4dbfc