VTTCue: Convert uses of std::pair<float, float> to FloatPoint

This is more in line with other code, and also semantically better (since
this is a point after all.) std::pair<double, double> is used in a few
places, but always converted from a float-pair, so convert those too.

BUG=448000

Review URL: https://codereview.chromium.org/859763004

git-svn-id: svn://svn.chromium.org/blink/trunk@188629 bbb929c8-8fbe-4397-9dbb-9b2b20218538
2 files changed