Fix subpixel metrics with GDI.

Fix subpixel metrics with GDI.

The previous code uncovered a rather strange issue with GDI, where it
appears that alternating between two HFONTs with the same attributes but
vastly different heights does not appear to invalidate the the 'x'
metrics (the 'y' metrics appear to be correct). As a result it is
possible to get completely useless results from GetGlyphOutlineW. This
change works around the issue by simply scaling the one font to the
required sizes, which also saves us an HFONT.

Committed: https://code.google.com/p/skia/source/detail?r=10425

[bungeman-skia, 2013-07-30 01:07:51]

Committed patchset #2 manually as r10425 (presubmit successful).