Add goog.string splitLines function.

Pull JS from string_test.html into string_test.js in this change.

R=nicksantos
DELTA=58 (58 added, 0 deleted, 0 changed)


Revision created by MOE tool push_codebase.
MOE_MIGRATION=6245


git-svn-id: http://closure-library.googlecode.com/svn/trunk@2499 0b95b8e8-c90f-11de-9d4f-f947ee5921c8