Mac: Add command line switch to force dark mode

Bug: 850098
Change-Id: I8d18484774982a8ec0272f62f0bd77a43668eb0d
Reviewed-on: https://chromium-review.googlesource.com/1238796Reviewed-by: ccameron <ccameron@chromium.org>
Reviewed-by: Mark Mentovai <mark@chromium.org>
Reviewed-by: Elly Fong-Jones <ellyjones@chromium.org>
Commit-Queue: Leonard Grey <lgrey@chromium.org>
Cr-Commit-Position: refs/heads/master@{#593347}

base/mac/sdk_forward_declarations.h

@@ -338,6 +338,20 @@ typedef NSString* VNBarcodeSymbology NS_STRING_ENUM;
 @end
 
 #endif  // MAC_OS_X_VERSION_10_13
+
+// Once Chrome no longer supports macOS 10.13, everything within this
+// preprocessor block can be removed.
+#if !defined(MAC_OS_X_VERSION_10_14) || \
+    MAC_OS_X_VERSION_MIN_REQUIRED < MAC_OS_X_VERSION_10_14
+
+@interface NSApplication (ForwardDeclare)
+@property(strong) NSAppearance* appearance;
+@end
+
+BASE_EXPORT extern NSString* const NSAppearanceNameDarkAqua;
+
+#endif
+
 // ----------------------------------------------------------------------------
 // The symbol for kCWSSIDDidChangeNotification is available in the
 // CoreWLAN.framework for OSX versions 10.6 through 10.10. The symbol is not

base/mac/sdk_forward_declarations.mm

@@ -18,3 +18,8 @@ NSString* const NSAppearanceNameVibrantDark = @"NSAppearanceNameVibrantDark";
     MAC_OS_X_VERSION_MIN_REQUIRED < MAC_OS_X_VERSION_10_11
 NSString* const CIDetectorTypeText = @"CIDetectorTypeText";
 #endif  // MAC_OS_X_VERSION_10_11
+
+#if !defined(MAC_OS_X_VERSION_10_14) || \
+    MAC_OS_X_VERSION_MIN_REQUIRED < MAC_OS_X_VERSION_10_14
+NSString* const NSAppearanceNameDarkAqua = @"NSAppearanceNameDarkAqua";
+#endif

chrome/browser/chrome_browser_application_mac.mm

@@ -8,6 +8,7 @@
 #include "base/command_line.h"
 #include "base/logging.h"
 #include "base/mac/call_with_eh_frame.h"
+#include "base/mac/sdk_forward_declarations.h"
 #include "base/observer_list.h"
 #include "base/strings/stringprintf.h"
 #include "base/strings/sys_string_conversions.h"
@@ -21,6 +22,7 @@
 #include "content/public/browser/browser_accessibility_state.h"
 #include "content/public/browser/native_event_processor_mac.h"
 #include "content/public/browser/native_event_processor_observer_mac.h"
+#include "ui/base/ui_base_switches.h"
 
 namespace chrome_browser_application_mac {
 
@@ -120,6 +122,12 @@ std::string DescriptionForNSEvent(NSEvent* event) {
 
 - (id)init {
   self = [super init];
+  if (base::CommandLine::ForCurrentProcess()->HasSwitch(
+          switches::kForceDarkMode)) {
+    if (@available(macOS 10.14, *)) {
+      self.appearance = [NSAppearance appearanceNamed:NSAppearanceNameDarkAqua];
+    }
+  }
 
   // Sanity check to alert if overridden methods are not supported.
   DCHECK([NSApplication

ui/base/ui_base_switches.cc

@@ -48,6 +48,9 @@ const char kEnableTouchDragDrop[] = "enable-touch-drag-drop";
 const char kEnableTouchableAppContextMenu[] =
     "enable-touchable-app-context-menus";
 
+// Forces dark mode in UI for platforms that support it.
+const char kForceDarkMode[] = "force-dark-mode";
+
 // Forces high-contrast mode in native UI drawing, regardless of system
 // settings. Note that this has limited effect on Windows: only Aura colors will
 // be switched to high contrast, not other system colors.

ui/base/ui_base_switches.h

@@ -27,6 +27,7 @@ UI_BASE_EXPORT extern const char kDisableTouchAdjustment[];
 UI_BASE_EXPORT extern const char kDisableTouchDragDrop[];
 UI_BASE_EXPORT extern const char kEnableTouchDragDrop[];
 UI_BASE_EXPORT extern const char kEnableTouchableAppContextMenu[];
+UI_BASE_EXPORT extern const char kForceDarkMode[];
 UI_BASE_EXPORT extern const char kForceHighContrast[];
 UI_BASE_EXPORT extern const char kLang[];
 UI_BASE_EXPORT extern const char kMaterialDesignInkDropAnimationSpeed[];