Fix threading issue in DirectWrite port initialization.

The DirectWrite port maintains a global instance of an IDWriteFactory,
which is used to create all other DirectWrite objects. However, the
initialization of this object is not currently thread safe.

R=caryclark@google.com

Review URL: https://codereview.chromium.org/107963003

git-svn-id: http://skia.googlecode.com/svn/trunk/src@12573 2bbb7eff-a529-9590-31e7-b0007b416f81
1 file changed