Use a common template for testing style data equivalency

Previously, we have many xxxDataEquivalent() functions that some are
same in logic and some are not optimized (e.g. not testing pointer
equivalency before value comparison).

Create a template function dataEquivalent and let the
xxxDataEquivalent() functions use it.

Review URL: https://codereview.chromium.org/269663005

git-svn-id: svn://svn.chromium.org/blink/trunk@173141 bbb929c8-8fbe-4397-9dbb-9b2b20218538