Make button fonts NORMAL weight on macOS 10.11 and 10.9.

Apple doesn't ship a MEDIUM weight font in 10.11 or 10.9. The font
system will upgrade it to BOLD (this is covered by tests in
platform_font_mac_unittests.mm). BOLD is too bold for buttons in UI,
so use a NORMAL weight.

Bug: 751414
Change-Id: I5dbac5a165120c919a92476f9fce6747c7e733c1
Reviewed-on: https://chromium-review.googlesource.com/597511
Commit-Queue: Trent Apted <tapted@chromium.org>
Reviewed-by: Peter Kasting <pkasting@chromium.org>
Cr-Commit-Position: refs/heads/master@{#491955}

chrome/browser/ui/views/harmony/harmony_typography_provider.cc

@@ -98,7 +98,7 @@ const gfx::FontList& HarmonyTypographyProvider::GetFont(int context,
 
   switch (context) {
     case views::style::CONTEXT_BUTTON_MD:
-      font_weight = WeightNotLighterThanNormal(gfx::Font::Weight::MEDIUM);
+      font_weight = MediumWeightForUI();
       break;
     case views::style::CONTEXT_DIALOG_TITLE:
       size_delta = kTitleSize - gfx::PlatformFont::kDefaultBaseFontSize;

ui/views/style/typography_provider.cc

@@ -5,11 +5,16 @@
 #include "ui/views/style/typography_provider.h"
 
 #include "base/logging.h"
+#include "build/build_config.h"
 #include "ui/base/default_style.h"
 #include "ui/base/resource/resource_bundle.h"
 #include "ui/native_theme/native_theme.h"
 #include "ui/views/style/typography.h"
 
+#if defined(OS_MACOSX)
+#include "base/mac/mac_util.h"
+#endif
+
 using gfx::Font;
 
 namespace views {
@@ -30,13 +35,27 @@ Font::Weight GetValueBolderThan(Font::Weight weight) {
 }  // namespace
 
 // static
-Font::Weight TypographyProvider::WeightNotLighterThanNormal(
-    Font::Weight weight) {
+Font::Weight TypographyProvider::MediumWeightForUI() {
+#if defined(OS_MACOSX)
+  // System fonts are not user-configurable on Mac, so there's a simpler check.
+  // However, 10.9 and 10.11 do not ship with a MEDIUM weight system font.  In
+  // that case, trying to use MEDIUM there will give a bold font, which will
+  // look worse with the surrounding NORMAL text than just using NORMAL.
+  return (base::mac::IsOS10_9() || base::mac::IsOS10_11())
+             ? Font::Weight::NORMAL
+             : Font::Weight::MEDIUM;
+#else
+  // NORMAL may already have at least MEDIUM weight. Return NORMAL in that case
+  // since trying to return MEDIUM would actually make the font lighter-weight
+  // than the surrounding text. For example, Windows can be configured to use a
+  // BOLD font for dialog text; deriving MEDIUM from that would replace the BOLD
+  // attribute with something lighter.
   if (ResourceBundle::GetSharedInstance()
           .GetFontListWithDelta(0, Font::NORMAL, Font::Weight::NORMAL)
-          .GetFontWeight() < weight)
-    return weight;
+          .GetFontWeight() < Font::Weight::MEDIUM)
+    return Font::Weight::MEDIUM;
   return Font::Weight::NORMAL;
+#endif
 }
 
 const gfx::FontList& DefaultTypographyProvider::GetFont(int context,
@@ -90,7 +109,7 @@ void DefaultTypographyProvider::GetDefaultFont(int context,
   switch (context) {
     case style::CONTEXT_BUTTON_MD:
       *size_delta = ui::kLabelFontSizeDelta;
-      *font_weight = WeightNotLighterThanNormal(Font::Weight::MEDIUM);
+      *font_weight = MediumWeightForUI();
       break;
     case style::CONTEXT_DIALOG_TITLE:
       *size_delta = ui::kTitleFontSizeDelta;

ui/views/style/typography_provider.h

@@ -37,13 +37,12 @@ class VIEWS_EXPORT TypographyProvider {
   // Gets the line spacing, or 0 if it should be provided by gfx::FontList.
   virtual int GetLineHeight(int context, int style) const = 0;
 
-  // The system may indicate a "bold" UI font is preferred (e.g. by selecting
-  // the "Bold" checkbox in Windows under "Change only the text size" in
-  // Control Panel). In this case, a user's gfx::Weight::NORMAL font will
-  // already be bold, and requesting a MEDIUM font will result in a font that is
-  // less bold. So this method returns NORMAL, if the NORMAL font is at least as
-  // bold as |weight|.
-  static gfx::Font::Weight WeightNotLighterThanNormal(gfx::Font::Weight weight);
+  // Returns the weight that will result in the ResourceBundle returning an
+  // appropriate "medium" weight for UI. This caters for systems that are known
+  // to be unable to provide a system font with weight other than NORMAL or BOLD
+  // and for user configurations where the NORMAL font is already BOLD. In both
+  // of these cases, NORMAL is returned instead.
+  static gfx::Font::Weight MediumWeightForUI();
 
  protected:
   TypographyProvider() = default;