Implement Harmony typography spec.

ui/gfx/platform_font.h

Index: ui/gfx/platform_font.h
diff --git a/ui/gfx/platform_font.h b/ui/gfx/platform_font.h
index 48e14cf99608ad0fb52cae9b2ef6b2763cb99f2f..20d622b310a5ce6fe333a3504bd3f3ffdc4a042d 100644
--- a/ui/gfx/platform_font.h
+++ b/ui/gfx/platform_font.h
@@ -21,6 +21,16 @@ struct FontRenderParams;
 
 class GFX_EXPORT PlatformFont : public base::RefCounted<PlatformFont> {
  public:
+// The size of the font returned by CreateDefault() on a "default" platform
+// configuration. This allows UI that wants to target a particular size of font
+// to obtain that size for the majority of users, while still compensating for a
+// user preference for a larger or smaller font.
+#if defined(OS_MACOSX)
+  static constexpr int kPopularDefaultFontSize = 13;

[Peter Kasting, 2017/04/06 06:17:07]

Nit: I have no idea where the word "popular" in this name comes from.  Maybe
kDefaultFontSize or kDefaultBaseFontSize or something.

[tapted, 2017/04/06 09:11:10]

heh, that was to try to distinguish it from "CreateDefault()" -- I didn't want
to imply that CreateDefault() is expected to return a font of kDefaultFontSize.
But I guess they are still related - I went for kDefaultBaseFontSize.

+#else
+  static constexpr int kPopularDefaultFontSize = 12;
+#endif
+
   // Creates an appropriate PlatformFont implementation.
   static PlatformFont* CreateDefault();
 #if defined(OS_WIN) || defined(OS_MACOSX) || defined(OS_IOS)