Try last resort on no-match in platformFallbackForCharacter on Android

On Android, some locale-preferred fonts (e.g. DroidSansFallback.ttf for
Chinese locale) doesn't contain all characters that the default locale
system fonts contain.

For characters that is missing in the font, fallback to the default
locale system font, by calling getLastResortFallbackFont() in
FontCache::platformFallbackForCharacter().

Also modified getLastResortFallbackFont() to prefer Skia default font
instead of the hard-coded default font (sans) and to map also cursive
and fantasy generic families.

Combined similar code in FontCacheSkia.cpp.

BUG=347121
TEST=FontCacheAndroid.platformFallbackForCharacter (will be enabled in another CL)
R=dglazkov@chromium.org

Review URL: https://codereview.chromium.org/185863007

git-svn-id: svn://svn.chromium.org/blink/trunk@168410 bbb929c8-8fbe-4397-9dbb-9b2b20218538