[Win, Linux] Always display the avatar button text at the same size.

ui/gfx/font_list.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_FONT_LIST_H_
 #define UI_GFX_FONT_LIST_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 65 matching lines @@
 
   // Returns a new FontList with the same font names and style but resized.
   // |size_delta| is the size in pixels to add to the current font size.
   FontList DeriveWithSizeDelta(int size_delta) const;
 
   // Returns a new FontList with the same font names and size but the given
   // style. |font_style| specifies the new style, which is a bitmask of the
   // values: Font::BOLD, Font::ITALIC and Font::UNDERLINE.
   FontList DeriveWithStyle(int font_style) const;
 
+  // Shrinks the font size until the font list fits within |height| while
+  // having its cap height vertically centered. Returns a new FontList with
+  // the correct height.
+  //
+  // The expected layout:
+  //   +--------+-----------------------------------------------+------------+
+  //   |        | y offset                                      | space      |
+  //   |        +--------+-------------------+------------------+ above      |
+  //   |        |        |                   | internal leading | cap height |
+  //   | box    | font   | ascent (baseline) +------------------+------------+
+  //   | height | height |                   | cap height                    |
+  //   |        |        |-------------------+------------------+------------+
+  //   |        |        | descent (height - baseline)          | space      |
+  //   |        +--------+--------------------------------------+ below      |
+  //   |        | space at bottom                               | cap height |
+  //   +--------+-----------------------------------------------+------------+
+  // Goal:
+  //     center of box height == center of cap height
+  //     (i.e. space above cap height == space below cap height)
+  // Restrictions:
+  //     y offset >= 0
+  //     space at bottom >= 0
+  //     (i.e. Entire font must be visible inside the box.)
+  gfx::FontList DeriveWithHeightUpperBound(int height) const;
+
   // Returns the height of this font list, which is max(ascent) + max(descent)
   // for all the fonts in the font list.
   int GetHeight() const;
 
   // Returns the baseline of this font list, which is max(baseline) for all the
   // fonts in the font list.
   int GetBaseline() const;
 
   // Returns the cap height of this font list.
   // Currently returns the cap height of the primary font.
@@ skipping 25 matching lines @@
   explicit FontList(FontListImpl* impl);
 
   static const scoped_refptr<FontListImpl>& GetDefaultImpl();
 
   scoped_refptr<FontListImpl> impl_;
 };
 
 }  // namespace gfx
 
 #endif  // UI_GFX_FONT_LIST_H_