PLATFORM(MAC) isn't defined for Chrome, so on OS X we're picking up the Windows version of cgColor() from ColorCG.cpp rather than the Mac version from ColorMac.mm.
The define needs to be changed to either use !PLATFORM(DARWIN) or PLATFORM(WIN) so Chrome on OS X doesn't pick up the Windows version.
https://bugs.webkit.org/show_bug.cgi?id=23512 also bears mentioning in this context.
Fixed in r41345
Jeremy, why did we want cgColor ColorMac.mm for mcChrome instead of ColorCG.cpp? I just helped Pam out with this for the merge (she'll probably contact you separately about focusRingColor), but I don't understand why you wanted this change, it seems like it's going in the wrong direction.