<rdar://problem/10475450> Synthetic bold is illegible under some scaling transforms

<rdar://problem/10475450> Synthetic bold is illegible under some scaling transforms
https://bugs.webkit.org/show_bug.cgi?id=78044

Reviewed by Beth Dakin.

Source/WebCore:

Tests: fast/text/synthetic-bold-transformed-expected.html
       fast/text/synthetic-bold-transformed.html

* platform/graphics/mac/FontMac.mm:
(WebCore::Font::drawGlyphs): Changed to interpret syntheticBoldOffset as a length in device pixels.

LayoutTests:

* fast/text/synthetic-bold-transformed-expected.html: Added.
* fast/text/synthetic-bold-transformed.html: Added.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@107012 268f45cc-cd09-0410-ab3c-d52691b4dbfc