fixup! Bug 41116: Normalize system fonts.

Update to the latest proposal to upstream.
It fixes build issues on macOS.

layout/base/nsLayoutUtils.cpp

@@ -9676,43 +9676,37 @@ already_AddRefed<nsFontMetrics> nsLayoutUtils::GetMetricsFor(
   return aPresContext->GetMetricsFor(font, params);
 }
 
-/* static */
-void nsLayoutUtils::ComputeSystemFont(nsFont* aSystemFont,
-                                      LookAndFeel::FontID aFontID,
-                                      const nsFont& aDefaultVariableFont,
-                                      const Document* aDocument) {
-  gfxFontStyle fontStyle;
-  nsAutoString systemFontName;
-  if (aDocument->ShouldResistFingerprinting()) {
+static void GetSpoofedSystemFontForRFP(LookAndFeel::FontID aFontID,
+                                       gfxFontStyle& aStyle, nsAString& aName) {
 #if defined(XP_MACOSX)
-    systemFontName = u"-apple-system"_ns;
+  aName = u"-apple-system"_ns;
   // Values taken from a macOS 10.15 system.
   switch (aFontID) {
     case LookAndFeel::FontID::Caption:
     case LookAndFeel::FontID::Menu:
-        fontStyle.size = 13;
+      aStyle.size = 13;
       break;
     case LookAndFeel::FontID::SmallCaption:
-        fontStyle.weight = gfxFontStyle::FontWeight(700);
+      aStyle.weight = gfxFontStyle::FontWeight::BOLD;
       // fall-through
     case LookAndFeel::FontID::MessageBox:
     case LookAndFeel::FontID::StatusBar:
-        fontStyle.size = 11;
+      aStyle.size = 11;
       break;
     default:
-        fontStyle.size = 12;
+      aStyle.size = 12;
       break;
   }
-#elif defined(XP_WIN) || defined(MOZ_WIDGET_ANDROID)
+#elif defined(XP_WIN)
   // Windows uses Segoe UI for Latin alphabets, but other fonts for some RTL
   // languages, so we fallback to sans-serif to fall back to the user's
   // default sans-serif. Size is 12px for all system fonts (tried in an en-US
   // system).
   // Several Android systems reported Roboto 12px, so similar to what Windows
   // does.
-    systemFontName = u"sans-serif"_ns;
-    fontStyle.size = 12;
-#else
+  aName = u"sans-serif"_ns;
+  aStyle.size = 12;
+#elif !defined(MOZ_WIDGET_ANDROID)
   // On Linux, there is not a default. For example, GNOME on Debian uses
   // Cantarell, 14.667px. Ubuntu Mate uses the Ubuntu font, but also 14.667px.
   // Fedora with KDE uses Noto Sans, 13.3333px, but it uses Noto Sans on
@@ -9720,9 +9714,21 @@ void nsLayoutUtils::ComputeSystemFont(nsFont* aSystemFont,
   // In general, Linux uses some sans-serif, but its size can vary between
   // 12px and 16px. We chose 15px because it is what Firefox is doing for the
   // UI font-size.
-    systemFontName = u"sans-serif"_ns;
-    fontStyle.size = 15;
+  aName = u"sans-serif"_ns;
+  aStyle.size = 15;
 #endif
+  // No need to do anything on Android, as font and sizes are already fixed.
+}
+
+/* static */
+void nsLayoutUtils::ComputeSystemFont(nsFont* aSystemFont,
+                                      LookAndFeel::FontID aFontID,
+                                      const nsFont& aDefaultVariableFont,
+                                      const Document* aDocument) {
+  gfxFontStyle fontStyle;
+  nsAutoString systemFontName;
+  if (aDocument->ShouldResistFingerprinting()) {
+    GetSpoofedSystemFontForRFP(aFontID, fontStyle, systemFontName);
   } else if (!LookAndFeel::GetFont(aFontID, systemFontName, fontStyle)) {
     return;
   }