'gasp' to control symmetric rendering on Windows.

Currently Skia tries hard to use symmetric rendering with DirectWrite
as often as possible. However, particularly on Windows 7 with CJK fonts,
thin horizontal strokes can be rendered without sufficient contrast
because the font was relying on the 6x1 oversampling for what is
effecitvely drop-out control. This change will only allow symmetric
rendering if the font allows it in the 'gasp' table.

BUG=chromium:645055

Change-Id: I45a9d5e4a0b49bb969c44fb20dc92528dfe9c48d
Reviewed-on: https://skia-review.googlesource.com/8268
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Ben Wagner <bungeman@google.com>
1 file changed