Merge virtual mac-antialiasedtext and windows-directwrite test suites

The virtual mac-antialiasedtext and windows-directwrite test suites
both test antialiased text and both use the same subsets of text.
Merge both into a new antialiasedtext test suite now that directwrite
is always enabled (for tests) on windows.

BUG=379590
R=dpranke@chromium.org

Review URL: https://codereview.chromium.org/303133007

git-svn-id: svn://svn.chromium.org/blink/trunk@175588 bbb929c8-8fbe-4397-9dbb-9b2b20218538