Change SimpleFontData::platformBoundsForGlyph to use getTextPath

On skia platforms we currnetly implement platformBoundsForGlyph by
using the measureText API. This returns a conservative bounding box
intended for paint but it is close enough to the actual metrics in
most cases. For vertical text however it tends to overly inflated.

Change it to use the getTextPath API instead which returns more
precise metrics instead for text metrics.

BUG=249099

Review URL: https://codereview.chromium.org/25045010

git-svn-id: svn://svn.chromium.org/blink/trunk@158584 bbb929c8-8fbe-4397-9dbb-9b2b20218538