ea84dd9118
Minikin layout uses a FontCollection containing a list of pre-selected fonts for a particular font family. This patch extends the FontCollection to invoke a hook provided by libtxt if layout sees a character that can not be rendered by any font in the collection. * Change the Minikin lock to a recursive mutex. This is required because the fallback font provider may create new fonts during a layout operation that already holds the lock. * Implement a fallback font provider hook that queries Skia for fonts matching an unrecognized character. * Maintain a cache of fallback fonts. Prepopulate the cache with fonts covering some commonly used character classes. * Add a last resort font list for cases where Skia's font manager can not find any font for a character (similar to Blink's FontCache::getLastResortFallbackFont)