Use correct color accessors when resolving styles.

The visitedDependentColor function probably shouldn't be used during
style recalc. Note this change is probably not testable at the moment
since testRunner.keepWebHistory is not implemented.

BUG=284357

Review URL: https://codereview.chromium.org/96163002

git-svn-id: svn://svn.chromium.org/blink/trunk@162870 bbb929c8-8fbe-4397-9dbb-9b2b20218538
WTF's unit test helpers should be usable from other unit tests in Blink.

This patch adds a new gyp target called "wtf_unittest_helpers", which should
contain unittest-only utilities for WTF types. The target can be used not only
from wtf_unittests but from other unit tests in Blink.

Originally, WTFTestHelpers was a header-only utility, thus it could be used
from any modules in Blink, including production codes. This patch tightens up
the situation a bit; if a function in wtf_unittest_helpers is used from
a non-unittest module, that will result a link error.

Unit-test only patch; no behavior change.

BUG=none
R=morrita@chromium.org

Review URL: https://codereview.chromium.org/90893004

git-svn-id: svn://svn.chromium.org/blink/trunk@162871 bbb929c8-8fbe-4397-9dbb-9b2b20218538