Isolate Early Warning System definitions into a JSON
https://bugs.webkit.org/show_bug.cgi?id=114558

Reviewed by Benjamin Poulain.

Added ews.json to common/config, and made tool/commands/__init__.py call
AbstractEarlyWarningSystem.load_ews_classes to instantiate classes based on ews.json.

* Scripts/webkitpy/common/config/ews.json: Extracted from earlywarningsystem.py.
* Scripts/webkitpy/tool/commands/__init__.py:
* Scripts/webkitpy/tool/commands/earlywarningsystem.py:
(AbstractEarlyWarningSystem):
(AbstractEarlyWarningSystem.__init__):
(AbstractEarlyWarningSystem.load_ews_classes): Added. Loads ews.json.
* Scripts/webkitpy/tool/commands/earlywarningsystem_unittest.py:
(EarlyWarningSystemTest._default_expected_logs):
(_test_ews):
(test_ewses):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@148498 268f45cc-cd09-0410-ab3c-d52691b4dbfc