adding baseline options for super/sub scripting

ui/gfx/text_constants.h

Index: ui/gfx/text_constants.h
diff --git a/ui/gfx/text_constants.h b/ui/gfx/text_constants.h
index 82f2a3b7061386b425c825480db256fe8c9ca446..c76adfa3a159c8a92b135c2ca45156736c547edd 100644
--- a/ui/gfx/text_constants.h
+++ b/ui/gfx/text_constants.h
@@ -42,6 +42,25 @@ enum TextStyle {
   NUM_TEXT_STYLES,
 };
 
+// Text baseline offset types.
+// Figure of font metrics:
+//   +--------+--------+------------------------+-------------+
+//   |        |        | internal leading       | SUPERSCRIPT |
+//   |        |        +------------+-----------|             |
+//   |        | ascent |            | SUPERIOR  |-------------+
+//   | height |        | cap height |-----------|
+//   |        |        |            | INFERIOR  |-------------+
+//   |        |--------+------------+-----------|             |
+//   |        | descent                         | SUBSCRIPT   |
+//   +--------+---------------------------------+-------------+
+enum BaselineStyle {
+  NORMAL_BASELINE = 0,
+  SUPERSCRIPT,  // e.g. a mathematical exponent would be superscript.
+  SUPERIOR,     // e.g. 8th, the "th" would be superior script.
+  INFERIOR,     // e.g. 1/2, the "2" would be inferior ("1" is superior).
+  SUBSCRIPT,    // e.g. H2O, the "2" would be subscript.
+};
+
 // Elision behaviors of text that exceeds constrained dimensions.
 enum ElideBehavior {
   NO_ELIDE = 0, // Do not modify the text, it may overflow its available bounds.