Use brave theme type as a system dark mode on Windows

Aligning base UI theme(ex, context menu) with brave theme was not
implemented on Windows because Windows doesn't support per-application
theme. Whereas, MacOS support it. So, when user set dark or light, it is
set as a application theme.
To solve this on Windows, NativeThemeWin::SystemDarkModeEnabled() checks
whether dark mode enabling is overridden or not.
Overridden value is set by client(BraveThemeService).

browser/themes/brave_theme_service.cc

@@ -27,6 +27,10 @@
 #include "ui/native_theme/native_theme.h"
 #include "ui/native_theme/native_theme_dark_aura.h"
 
+#if defined(OS_WIN)
+#include "ui/native_theme/native_theme_win.h"
+#endif
+
 namespace {
 BraveThemeType GetThemeTypeBasedOnChannel() {
   switch (chrome::GetChannel()) {
@@ -151,6 +155,9 @@ void BraveThemeService::Init(Profile* profile) {
   if (profile->GetPrefs()->FindPreference(kBraveThemeType)) {
     RecoverPrefStates(profile);
     OverrideDefaultThemeIfNeeded(profile);
+#if defined(OS_WIN)
+    OverrideSystemDarkModeIfNeeded(profile);
+#endif
     if (SystemThemeModeEnabled()) {
       // Start with proper system theme to make brave theme and
       // base ui components theme use same theme.
@@ -203,7 +210,10 @@ void BraveThemeService::OnPreferenceChanged(const std::string& pref_name) {
     SetSystemTheme(static_cast<BraveThemeType>(
         profile()->GetPrefs()->GetInteger(kBraveThemeType)));
   }
+#elif defined(OS_WIN)
+  OverrideSystemDarkModeIfNeeded(profile());
 #endif
+
   if (notify_theme_observer_here) {
     // Notify dark (cross-platform) and light (platform-specific) variants
     // When theme is changed from light to dark, we notify to light theme
@@ -234,6 +244,21 @@ void BraveThemeService::OverrideDefaultThemeIfNeeded(Profile* profile) {
   }
 }
 
+#if defined(OS_WIN)
+void BraveThemeService::OverrideSystemDarkModeIfNeeded(Profile* profile) {
+  if (SystemThemeModeEnabled()) {
+    BraveThemeType type = static_cast<BraveThemeType>(
+        profile->GetPrefs()->GetInteger(kBraveThemeType));
+    // Overrides system dark mode only when brave theme type is not
+    // "Same as Windows". In this case, follow os theme.
+    // Otherwise, use brave theme as a native theme regardless of os theme.
+    ui::SetOverrideSystemDarkMode(
+        type != BraveThemeType::BRAVE_THEME_TYPE_DEFAULT,
+        type == BraveThemeType::BRAVE_THEME_TYPE_DARK);
+  }
+}
+#endif
+
 void BraveThemeService::SetBraveThemeEventRouterForTesting(
     extensions::BraveThemeEventRouter* mock_router) {
   brave_theme_event_router_.reset(mock_router);

browser/themes/brave_theme_service.h

@@ -64,6 +64,9 @@ class BraveThemeService : public ThemeService {
 
   void RecoverPrefStates(Profile* profile);
   void OverrideDefaultThemeIfNeeded(Profile* profile);
+#if defined(OS_WIN)
+  void OverrideSystemDarkModeIfNeeded(Profile* profile);
+#endif
 
   static bool SystemThemeModeEnabled();
 

browser/themes/brave_theme_service_browsertest.cc

@@ -121,10 +121,8 @@ IN_PROC_BROWSER_TEST_F(BraveThemeServiceTest, NativeThemeObserverTest) {
   SetBraveThemeType(profile, BraveThemeType::BRAVE_THEME_TYPE_LIGHT);
 }
 
-#if defined(OS_MACOSX)
+#if defined(OS_MACOSX) || defined(OS_WIN)
 IN_PROC_BROWSER_TEST_F(BraveThemeServiceTest, SystemThemeChangeTest) {
-  // TODO(simonhong): Delete this when we gets dark mode enabled branch on
-  // MacOS.
   if (!BraveThemeService::SystemThemeModeEnabled())
     return;
 

chromium_src/ui/native_theme/native_theme_win.cc

@@ -4,10 +4,12 @@
  * You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #include "ui/native_theme/native_theme_dark_aura.h"
+#include "ui/native_theme/native_theme_win.h"
 
-void NotifyProperThemeObserver();
+namespace {
 
-#include "../../../../ui/native_theme/native_theme_win.cc"  // NOLINT
+bool system_dark_mode_overridden = false;
+bool dark_mode_enabled = false;
 
 // TODO(simonhong): Move this function to ui namespace to share with
 // native_theme_mac.mm.
@@ -18,3 +20,26 @@ void NotifyProperThemeObserver() {
       ? ui::NativeTheme::GetInstanceForNativeUi()->NotifyObservers()
       : ui::NativeThemeDarkAura::instance()->NotifyObservers();
 }
+
+bool OverrideSystemDarkMode() {
+  return system_dark_mode_overridden;
+}
+
+bool GetSystemDarkModeEnabledOverrides() {
+  return dark_mode_enabled;
+}
+
+}  // namespace
+
+#include "../../../../ui/native_theme/native_theme_win.cc"  // NOLINT
+
+namespace ui {
+
+void SetOverrideSystemDarkMode(bool override,
+                               bool enable_dark_mode) {
+  system_dark_mode_overridden = override;
+  dark_mode_enabled = enable_dark_mode;
+}
+
+}  // namespace ui
+

chromium_src/ui/native_theme/native_theme_win.h

@@ -0,0 +1,21 @@
+/* Copyright (c) 2019 The Brave Authors. All rights reserved.
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "../../../../ui/native_theme/native_theme_win.h"
+
+// Custom header guard is used to avoid including function declaration multiple
+// times.
+#ifndef UI_NATIVE_THEME_NATIVE_THEME_WIN_H_BRAVE_  // NOLINT
+#define UI_NATIVE_THEME_NATIVE_THEME_WIN_H_BRAVE_  // NOLINT
+
+namespace ui {
+
+// If |override| is true, system dark mode is overridden by |enable_dark_mode|.
+// If |override| is false, |enable_dark_mode| is ignored.
+void NATIVE_THEME_EXPORT SetOverrideSystemDarkMode(bool override,
+                                                   bool enable_dark_mode);
+}  // namespace ui
+
+#endif  // UI_NATIVE_THEME_NATIVE_THEME_WIN_H_BRAVE_  // NOLINT

patches/ui-native_theme-native_theme_win.cc.patch

@@ -1,8 +1,16 @@
 diff --git a/ui/native_theme/native_theme_win.cc b/ui/native_theme/native_theme_win.cc
-index 0df107bf9757a81897e9312a9eba977b8a173646..61e4f4ce671c5e0f92208b54aade903110ddc7a7 100644
+index 0df107bf9757a81897e9312a9eba977b8a173646..760ea5114e984b4536b2f894f8e7a2fb1a24b372 100644
 --- a/ui/native_theme/native_theme_win.cc
 +++ b/ui/native_theme/native_theme_win.cc
-@@ -1934,7 +1934,11 @@ void NativeThemeWin::RegisterThemeRegkeyObserver() {
+@@ -592,6 +592,7 @@ bool NativeThemeWin::SystemDarkModeEnabled() const {
+   // ...unless --force-dark-mode was specified in which case caveat emptor.
+   if (UsesHighContrastColors() && !NativeTheme::SystemDarkModeEnabled())
+     return false;
++  if (OverrideSystemDarkMode()) return GetSystemDarkModeEnabledOverrides();
+   bool fDarkModeEnabled = false;
+   if (hkcu_themes_regkey_.Valid()) {
+     DWORD apps_use_light_theme = 1;
+@@ -1934,7 +1935,11 @@ void NativeThemeWin::RegisterThemeRegkeyObserver() {
    DCHECK(hkcu_themes_regkey_.Valid());
    hkcu_themes_regkey_.StartWatching(base::BindOnce(
        [](NativeThemeWin* native_theme) {