Fix Skia FontCache platform data construction to use right font size
    
The skia version of FontCache::createFontPlatformData incorrectly used
fontDescription.computedSize instead of computedPixelSize even if sub-
pixel font scaling wasn't enabled. This could cause an entry with the
wrong size to be added to the FontCache.
    
Originally landed as r159122 but rolled out in r159185 due to a flaky
android test.
    
BUG=304986

Review URL: https://codereview.chromium.org/26641003

git-svn-id: svn://svn.chromium.org/blink/trunk@159614 bbb929c8-8fbe-4397-9dbb-9b2b20218538