Add test for typeface style round trip.

src/core/SkFontStyle.cpp

Index: src/core/SkFontStyle.cpp
diff --git a/src/core/SkFontStyle.cpp b/src/core/SkFontStyle.cpp
index 01628ae9d9d4ccdceb774ec31ab591f53cb7d9f6..c6de81885fc9222cf49166b34e964e552df83003 100644
--- a/src/core/SkFontStyle.cpp
+++ b/src/core/SkFontStyle.cpp
@@ -18,7 +18,7 @@ SkFontStyle::SkFontStyle() {
 
 SkFontStyle::SkFontStyle(int weight, int width, Slant slant) {
     fUnion.fU32 = 0;
-    fUnion.fR.fWeight = SkTPin<int>(weight, kThin_Weight, kBlack_Weight);
+    fUnion.fR.fWeight = SkTPin<int>(weight, 0, 1000);

[reed1, 2016/07/25 16:48:50]

expose as kMin_Weight and kMax_Weight ?

[bungeman-skia, 2016/07/25 21:03:58]

For 1000 it seems best to use kExtraBlack_Weight. Most systems seem to use the
terms 'extra black' or 'ultra black' for this (as synonyms), but I lean toward
'extra' as the current naming convention is that 'extra' is used in weight names
and 'ultra' in width names.

As for 0, existing naming seems some more confused. FontConfig actually doesn't
even have a setting for this it seems, it just bottoms out at 'Thin'. It seems
others just stick with 'Thin' being 100 and just describe it as the 'lightest'
weight. In some sense 0 implies that effectively nothing is drawn. Also,
usWeightClass is an unsigned short, so 0 really is as low as it goes (as opposed
to 1000 which is somewhat arbitrary). As a result kInvisible_Weight seems like a
good name.

     fUnion.fR.fWidth = SkTPin<int>(width, kUltraCondensed_Width, kUltaExpanded_Width);
     fUnion.fR.fSlant = SkTPin<int>(slant, kUpright_Slant, kOblique_Slant);
 }