Fixed font height on OS X. Also added some unittests.

app/gfx/font_mac.mm

 // Copyright (c) 2009 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.
 
 #include "app/gfx/font.h"
 
 #include <Cocoa/Cocoa.h>
 
 #include "base/logging.h"
+#include "base/scoped_nsobject.h"
 #include "base/sys_string_conversions.h"
 
 namespace gfx {
 
 // static
 Font Font::CreateFont(const std::wstring& font_name, int font_size) {
   return Font(font_name, font_size, NORMAL);
 }
 
 Font::Font(const std::wstring& font_name, int font_size, int style)
     : font_name_(font_name),
       font_size_(font_size),
       style_(style) {
   calculateMetrics();
 }
 
 Font::Font()
     : font_size_([NSFont systemFontSize]),
       style_(NORMAL) {
   NSFont* system_font = [NSFont systemFontOfSize:font_size_];
   font_name_ = base::SysNSStringToWide([system_font fontName]);
   calculateMetrics();
 }
 
 void Font::calculateMetrics() {
   NSFont* font = nativeFont();
-  // TODO(akalin): This is the wrong height to use!  Use either the height
-  // of the bounding rect for the font or ascender - descender; this needs
-  // further investigation.  Width may be wrong, too.
-  height_ = [font xHeight];
+  scoped_nsobject<NSLayoutManager> layout_manager(
+      [[NSLayoutManager alloc] init]);
+  height_ = [layout_manager defaultLineHeightForFont:font];
   ascent_ = [font ascender];
   avg_width_ = [font boundingRectForGlyph:[font glyphWithName:@"x"]].size.width;
 }
 
 Font Font::DeriveFont(int size_delta, int style) const {
   return Font(font_name_, font_size_ + size_delta, style);
 }
 
 int Font::height() const {
   return height_;
@@ skipping 34 matching lines @@
 
 NativeFont Font::nativeFont() const {
   // TODO(pinkerton): apply |style_| to font.
   // We could cache this, but then we'd have to conditionally change the
   // dtor just for MacOS. Not sure if we want to/need to do that.
   return [NSFont fontWithName:base::SysWideToNSString(font_name_)
                          size:font_size_];
 }
 
 }  // namespace gfx