From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Samuel Attard <sattard@slack-corp.com>
Date: Mon, 26 Aug 2019 14:32:41 -0700
Subject: feat: add set_theme_source to allow apps to override chromiums
 internal theme choice

This patch is required as Chromium doesn't currently let folks using
//ui override the theme choice in NativeTheme.  It defaults to
respecting the OS theme choice and some apps don't always want to do
that.  With this patch we can override the theme value that Chromium
uses internally for things like menus and devtools.

We can remove this patch once it has in some shape been upstreamed.

diff --git a/ui/native_theme/native_theme.cc b/ui/native_theme/native_theme.cc
index 6f9221b95d5609d6bc3395bd3a3c81670877fdd0..bd4cd7cf50ea7f8816b35b3150bea8c459571231 100644
--- a/ui/native_theme/native_theme.cc
+++ b/ui/native_theme/native_theme.cc
@@ -257,6 +257,8 @@ NativeTheme::NativeTheme(bool should_use_dark_colors)
 NativeTheme::~NativeTheme() = default;
 
 bool NativeTheme::ShouldUseDarkColors() const {
+  if (theme_source() == ThemeSource::kForcedLight) return false;
+  if (theme_source() == ThemeSource::kForcedDark) return true;
   return should_use_dark_colors_;
 }
 
diff --git a/ui/native_theme/native_theme.h b/ui/native_theme/native_theme.h
index d254838cfb21ec2135691b84fd0432cbdbb92e24..f6a6e48ddd93ed1026cf216a59fa4a4d3d0b56d6 100644
--- a/ui/native_theme/native_theme.h
+++ b/ui/native_theme/native_theme.h
@@ -402,6 +402,22 @@ class NATIVE_THEME_EXPORT NativeTheme {
       ColorId color_id,
       ColorScheme color_scheme = ColorScheme::kDefault) const;
 
+  enum ThemeSource {
+    kSystem,
+    kForcedDark,
+    kForcedLight,
+  };
+
+  ThemeSource theme_source() const {
+    return theme_source_;
+  }
+
+  void set_theme_source(ThemeSource theme_source) {
+    bool original = ShouldUseDarkColors();
+    theme_source_ = theme_source;
+    if (ShouldUseDarkColors() != original) NotifyObservers();
+  }
+
   // Returns a shared instance of the native theme that should be used for web
   // rendering. Do not use it in a normal application context (i.e. browser).
   // The returned object should not be deleted by the caller. This function is
@@ -552,6 +568,7 @@ class NATIVE_THEME_EXPORT NativeTheme {
   bool forced_colors_ = false;
   PreferredColorScheme preferred_color_scheme_ = PreferredColorScheme::kLight;
   PreferredContrast preferred_contrast_ = PreferredContrast::kNoPreference;
+  ThemeSource theme_source_ = ThemeSource::kSystem;
 
   DISALLOW_COPY_AND_ASSIGN(NativeTheme);
 };
diff --git a/ui/native_theme/native_theme_win.cc b/ui/native_theme/native_theme_win.cc
index f4dff8de98066ea0ee4fb30ce832b27707791743..3d8c850111c0bbcd724c752e5b717ee46cfd5852 100644
--- a/ui/native_theme/native_theme_win.cc
+++ b/ui/native_theme/native_theme_win.cc
@@ -741,6 +741,8 @@ bool NativeThemeWin::ShouldUseDarkColors() const {
   // ...unless --force-dark-mode was specified in which case caveat emptor.
   if (InForcedColorsMode() && !IsForcedDarkMode())
     return false;
+  if (theme_source() == ThemeSource::kForcedLight) return false;
+  if (theme_source() == ThemeSource::kForcedDark) return true;
   return NativeTheme::ShouldUseDarkColors();
 }