dark_mode: Help keeping UI elements' current colors.

- Add DeprecatedGet*LayerColor functions in a separate file to help
  keeping UI elements' current colors before launching dark/light mode.

- Add ScopedLightModeAsDefeault to set the default color mode to light.
  This is done to support UI elements are light by default. E.g. Power
  button menu.

Bug: 1133952
Change-Id: I169f13991a649a1d1aacea451a6fb8ba8001396c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2440661
Commit-Queue: Min Chen <minch@chromium.org>
Reviewed-by: Ahmed Fakhry <afakhry@chromium.org>
Cr-Commit-Position: refs/heads/master@{#813003}

ash/BUILD.gn

@@ -831,6 +831,11 @@ component("ash") {
     "sticky_keys/sticky_keys_state.h",
     "style/ash_color_provider.cc",
     "style/ash_color_provider.h",
+    "style/default_color_constants.h",
+    "style/default_colors.cc",
+    "style/default_colors.h",
+    "style/scoped_light_mode_as_default.cc",
+    "style/scoped_light_mode_as_default.h",
     "system/accessibility/accessibility_feature_disable_dialog.cc",
     "system/accessibility/accessibility_feature_disable_dialog.h",
     "system/accessibility/accessibility_feature_pod_controller.cc",

ash/style/ash_color_provider.cc

@@ -299,6 +299,9 @@ void AshColorProvider::RemoveObserver(ColorModeObserver* observer) {
 }
 
 bool AshColorProvider::IsDarkModeEnabled() const {
+  if (override_light_mode_as_default_)
+    return false;
+
   if (!active_user_pref_service_)
     return kDefaultDarkModeEnabled;
   return active_user_pref_service_->GetBoolean(prefs::kDarkModeEnabled);

ash/style/ash_color_provider.h

@@ -207,6 +207,8 @@ class ASH_EXPORT AshColorProvider : public SessionObserver {
   SkColor GetLoginBackgroundBaseColor() const;
 
  private:
+  friend class ScopedLightModeAsDefault;
+
   // Gets the background default color.
   SkColor GetBackgroundDefaultColor() const;
 
@@ -222,6 +224,13 @@ class ASH_EXPORT AshColorProvider : public SessionObserver {
   // Notifies all the observers on |kColorModeThemed|'s change.
   void NotifyColorModeThemedPrefChange();
 
+  // Default color mode is dark, which is controlled by pref |kDarkModeEnabled|
+  // currently. But we can also override it to light through
+  // ScopedLightModeAsDefault. This is done to help keeping some of the UI
+  // elements as light by default before launching dark/light mode. This will be
+  // removed once enabling dark/light mode.
+  bool override_light_mode_as_default_ = false;
+
   base::ObserverList<ColorModeObserver> observers_;
   std::unique_ptr<PrefChangeRegistrar> pref_change_registrar_;
   PrefService* active_user_pref_service_ = nullptr;  // Not owned.

ash/style/default_color_constants.h

+// Copyright 2020 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef ASH_STYLE_DEFAULT_COLOR_CONSTANTS_H_
+#define ASH_STYLE_DEFAULT_COLOR_CONSTANTS_H_
+
+// Colors that can't be found in AshColorProvider. This is used to keep the UI
+// element's current look before launching dark/light mode. Using this together
+// with the Deprecated* functions inside default_colors.h file. Note: This file
+// will be removed once enabled dark/light mode.
+
+#endif  // ASH_STYLE_DEFAULT_COLOR_CONSTANTS_H_

ash/style/default_colors.cc

+// Copyright 2020 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "ash/style/default_colors.h"
+
+#include "ash/public/cpp/ash_features.h"
+
+namespace ash {
+
+SkColor DeprecatedGetShieldLayerColor(AshColorProvider::ShieldLayerType type,
+                                      SkColor default_color) {
+  if (!features::IsDarkLightModeEnabled())
+    return default_color;
+
+  return AshColorProvider::Get()->GetShieldLayerColor(type);
+}
+
+SkColor DeprecatedGetBaseLayerColor(AshColorProvider::BaseLayerType type,
+                                    SkColor default_color) {
+  if (!features::IsDarkLightModeEnabled())
+    return default_color;
+
+  return AshColorProvider::Get()->GetBaseLayerColor(type);
+}
+
+SkColor DeprecatedGetControlsLayerColor(
+    AshColorProvider::ControlsLayerType type,
+    SkColor default_color) {
+  if (!features::IsDarkLightModeEnabled())
+    return default_color;
+
+  return AshColorProvider::Get()->GetControlsLayerColor(type);
+}
+
+SkColor DeprecatedGetContentLayerColor(AshColorProvider::ContentLayerType type,
+                                       SkColor default_color) {
+  if (!features::IsDarkLightModeEnabled())
+    return default_color;
+
+  return AshColorProvider::Get()->GetContentLayerColor(type);
+}
+
+}  // namespace ash

ash/style/default_colors.h

+// Copyright 2020 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef ASH_STYLE_DEFAULT_COLORS_H_
+#define ASH_STYLE_DEFAULT_COLORS_H_
+
+#include "ash/style/ash_color_provider.h"
+#include "third_party/skia/include/core/SkColor.h"
+
+namespace ash {
+
+// APIs to help keeping the UI element's current color before launching
+// dark/light mode. |default_color| will be returned if the dark mode feature is
+// not enabled. Use these functions if the |default_color| can't be found in
+// AshColorProvider. And move |default_color| to default_color_constants.h file
+// to benefit future maintenance.
+SkColor DeprecatedGetShieldLayerColor(AshColorProvider::ShieldLayerType type,
+                                      SkColor default_color);
+SkColor DeprecatedGetBaseLayerColor(AshColorProvider::BaseLayerType type,
+                                    SkColor default_color);
+SkColor DeprecatedGetControlsLayerColor(
+    AshColorProvider::ControlsLayerType type,
+    SkColor default_color);
+SkColor DeprecatedGetContentLayerColor(AshColorProvider::ContentLayerType type,
+                                       SkColor default_color);
+}  // namespace ash
+
+#endif  // ASH_STYLE_DEFAULT_COLORS_H_

ash/style/scoped_light_mode_as_default.cc

+// Copyright 2020 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "ash/style/scoped_light_mode_as_default.h"
+
+#include "ash/style/ash_color_provider.h"
+
+namespace ash {
+
+ScopedLightModeAsDefault::ScopedLightModeAsDefault()
+    : previous_override_light_mode_as_default_(
+          AshColorProvider::Get()->override_light_mode_as_default_) {
+  AshColorProvider::Get()->override_light_mode_as_default_ = true;
+}
+
+ScopedLightModeAsDefault::~ScopedLightModeAsDefault() {
+  AshColorProvider::Get()->override_light_mode_as_default_ =
+      previous_override_light_mode_as_default_;
+}
+
+}  // namespace ash

ash/style/scoped_light_mode_as_default.h

+// Copyright 2020 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef ASH_STYLE_SCOPED_LIGHT_MODE_AS_DEFAULT_H_
+#define ASH_STYLE_SCOPED_LIGHT_MODE_AS_DEFAULT_H_
+
+namespace ash {
+
+// A helper class to set default color mode to light. Color mode is dark by
+// default, which is controlled by pref |kDarkModeEnabled| currently. Some of
+// the components need to be kept as LIGHT by default before launching
+// dark/light mode. E.g. power button menu and system toast.
+class ScopedLightModeAsDefault {
+ public:
+  ScopedLightModeAsDefault();
+  ScopedLightModeAsDefault(const ScopedLightModeAsDefault&) = delete;
+  ScopedLightModeAsDefault& operator=(const ScopedLightModeAsDefault&) = delete;
+  ~ScopedLightModeAsDefault();
+
+ private:
+  // Value of |override_light_mode_as_default_| inside AshColorProvider before
+  // setting.
+  bool previous_override_light_mode_as_default_;
+};
+
+}  // namespace ash
+
+#endif  // ASH_STYLE_SCOPED_LIGHT_MODE_AS_DEFAULT_H_