Fix hash collision of FontCacheKey

Use bits 8-9 of FontCacheKey::m_options for synthetic bold and synthetic
italic instead of bits 7-8, because bits 6-7 are used for smoothing
(see FontDescription::cacheKey()).

This fixes fast/css/font-smoothing.html flakiness after r162592.
FontCache for gFontPlatformDataCache collided in the test and
fast/css/font-face-synthetic-bold-italic-for-locally-installed.html.

TEST=fast/css/font-face-synthetic-bold-italic-for-locally-installed.html,fast/css/font-smoothing.html

Review URL: https://codereview.chromium.org/85403002

git-svn-id: svn://svn.chromium.org/blink/trunk@162636 bbb929c8-8fbe-4397-9dbb-9b2b20218538