Const-correctness in PDF drawText() call

If SkPDFDevice::drawText is called with glyph encoding and a font with
cubic outlines (CFF or Type1) and a glyph code > 255 then it was
mutating the in(const) glyph codes in place.  Instead, a copy is made.

BUG=skia:3019

Review URL: https://codereview.chromium.org/656143002
1 file changed