Add method to query system dark mode status in NativeTheme

Bug: 850098, 893598
Change-Id: I0ec85e12ae0714974e4d8122914afe330ac0fe93
Reviewed-on: https://chromium-review.googlesource.com/c/1240172Reviewed-by: Avi Drissman <avi@chromium.org>
Reviewed-by: Elly Fong-Jones <ellyjones@chromium.org>
Reviewed-by: Peter Kasting <pkasting@chromium.org>
Commit-Queue: Leonard Grey <lgrey@chromium.org>
Cr-Commit-Position: refs/heads/master@{#600008}

base/mac/sdk_forward_declarations.h

@@ -344,11 +344,19 @@ typedef NSString* VNBarcodeSymbology NS_STRING_ENUM;
 #if !defined(MAC_OS_X_VERSION_10_14) || \
     MAC_OS_X_VERSION_MIN_REQUIRED < MAC_OS_X_VERSION_10_14
 
+typedef NSString* NSAppearanceName;
+
 @interface NSApplication (ForwardDeclare)
 @property(strong) NSAppearance* appearance;
+@property(readonly, strong) NSAppearance* effectiveAppearance;
+@end
+
+@interface NSAppearance (ForwardDeclare)
+- (NSAppearanceName)bestMatchFromAppearancesWithNames:
+    (NSArray<NSAppearanceName>*)appearances;
 @end
 
-BASE_EXPORT extern NSString* const NSAppearanceNameDarkAqua;
+BASE_EXPORT extern NSAppearanceName const NSAppearanceNameDarkAqua;
 
 #endif
 

ui/native_theme/native_theme.cc

@@ -6,6 +6,8 @@
 
 #include <cstring>
 
+#include "base/command_line.h"
+#include "ui/base/ui_base_switches.h"
 #include "ui/native_theme/native_theme_observer.h"
 
 namespace ui {
@@ -47,4 +49,9 @@ NativeTheme::NativeTheme()
 
 NativeTheme::~NativeTheme() {}
 
+bool NativeTheme::SystemDarkModeEnabled() const {
+  return base::CommandLine::ForCurrentProcess()->HasSwitch(
+      switches::kForceDarkMode);
+}
+
 }  // namespace ui

ui/native_theme/native_theme.h

@@ -408,6 +408,9 @@ class NATIVE_THEME_EXPORT NativeTheme {
   // system accessibility settings and the system theme.
   virtual bool UsesHighContrastColors() const = 0;
 
+  // Whether OS-level dark mode (as in macOS Mojave or Windows 10) is enabled.
+  virtual bool SystemDarkModeEnabled() const;
+
  protected:
   NativeTheme();
   virtual ~NativeTheme();

ui/native_theme/native_theme_mac.h

@@ -47,6 +47,7 @@ class NATIVE_THEME_EXPORT NativeThemeMac : public NativeThemeBase {
       const gfx::Rect& rect,
       const MenuItemExtraParams& menu_item) const override;
   bool UsesHighContrastColors() const override;
+  bool SystemDarkModeEnabled() const override;
 
   // Paints the styled button shape used for default controls on Mac. The basic
   // style is used for dialog buttons, comboboxes, and tabbed pane tabs.

ui/native_theme/native_theme_mac.mm

@@ -196,6 +196,17 @@ bool NativeThemeMac::UsesHighContrastColors() const {
   return false;
 }
 
+bool NativeThemeMac::SystemDarkModeEnabled() const {
+  if (@available(macOS 10.14, *)) {
+    NSAppearanceName appearance =
+        [[NSApp effectiveAppearance] bestMatchFromAppearancesWithNames:@[
+          NSAppearanceNameAqua, NSAppearanceNameDarkAqua
+        ]];
+    return [appearance isEqual:NSAppearanceNameDarkAqua];
+  }
+  return NativeThemeBase::SystemDarkModeEnabled();
+}
+
 NativeThemeMac::NativeThemeMac() {
 }
 

ui/views/view_unittest.cc

@@ -4814,6 +4814,7 @@ class TestNativeTheme : public ui::NativeTheme {
     return gfx::Rect();
   }
   bool UsesHighContrastColors() const override { return false; }
+  bool SystemDarkModeEnabled() const override { return false; }
 
  private:
   DISALLOW_COPY_AND_ASSIGN(TestNativeTheme);