Fix font height on Mac with Helvetica Neue at size 16 (ResourceBundle::MediumFont)

ui/gfx/platform_font_mac.mm

Index: ui/gfx/platform_font_mac.mm
diff --git a/ui/gfx/platform_font_mac.mm b/ui/gfx/platform_font_mac.mm
index 892d2ea66d8a0be0b501b838a07516bfd5e5c0d7..008c4d049f11d8c58695a5d2a517f1ac59948263 100644
--- a/ui/gfx/platform_font_mac.mm
+++ b/ui/gfx/platform_font_mac.mm
@@ -166,11 +166,18 @@ void PlatformFontMac::CalculateMetricsAndInitRenderParams() {
     return;
   }
 
-  base::scoped_nsobject<NSLayoutManager> layout_manager(
-      [[NSLayoutManager alloc] init]);
-  height_ = SkScalarCeilToInt([layout_manager defaultLineHeightForFont:font]);
-  ascent_ = SkScalarCeilToInt([font ascender]);
-  cap_height_ = SkScalarCeilToInt([font capHeight]);
+  ascent_ = ceil([font ascender]);

[tapted, 2015/07/27 03:58:57]

note I ditched SkScalarCeilToInt here, just because since mac became 64-bit,
CGFloat is now a double. SkScalar remains a float, so I don't think it makes
sense to convert to a float before rounding. (and when SkScalar is a double,
SkScalarCeilToInt is just `(int)ceil(value)`). This wasn't because of any
particular failure, but makes me happier about the float conversions the test is
relying on.

+  cap_height_ = ceil([font capHeight]);
+
+  // PlatformFontMac once used -[NSLayoutManager defaultLineHeightForFont:] to
+  // initialize |height_|. However, it has a silly rounding bug. Essentially, it
+  // gives round(ascent) + round(descent). E.g. Helvetica Neue at size 16 gives
+  // ascent=15.4634, descent=3.38208 -> 15 + 3 = 18. When the height should be
+  // at least 19. According to the OpenType specification, these values should
+  // simply be added, so do that. Note this uses the already-rounded |ascent_|
+  // to ensure GetBaseline() + descender fits within GetHeight() during layout.
+  height_ = ceil(ascent_ + std::abs([font descender]) + [font leading]);
+
   average_width_ =
       NSWidth([font boundingRectForGlyph:[font glyphWithName:@"x"]]);