adding baseline options for super/sub scripting

ui/gfx/text_constants.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef UI_GFX_TEXT_CONSTANTS_H_
 #define UI_GFX_TEXT_CONSTANTS_H_
 
 namespace gfx {
 
 // TODO(msw): Distinguish between logical character stops and glyph stops?
@@ skipping 24 matching lines @@
 // TODO(msw): Merge with gfx::Font::FontStyle.
 enum TextStyle {
   BOLD = 0,
   ITALIC,
   STRIKE,
   DIAGONAL_STRIKE,
   UNDERLINE,
   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.
   TRUNCATE,     // Do not elide or fade, just truncate at the end of the string.
   ELIDE_HEAD,   // Add an ellipsis at the start of the string.
   ELIDE_MIDDLE, // Add an ellipsis in the middle of the string.
   ELIDE_TAIL,   // Add an ellipsis at the end of the string.
   ELIDE_EMAIL,  // Add ellipses to username and domain substrings.
   FADE_TAIL,    // Fade the string's end opposite of its horizontal alignment.
 };
 
 }  // namespace gfx
 
 #endif  // UI_GFX_TEXT_CONSTANTS_H_