Do not cache dark mode settings.

It is unclear whether caching the settings improved performance. The
performance regression resolved before the CL adding the caches
landed, and there was no significant improvement to performance once
the CL did land.

However, it did make the code less clear and introduced greater
potential for bugs (e.g. https://crbug.com/1002664).

Bug: 991838
Change-Id: Ia67a693596ead2a3b392b6e1835e0a2963f47d84
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1822477Reviewed-by: Rune Lillesveen <futhark@chromium.org>
Commit-Queue: Aran Gilman <gilmanmh@google.com>
Cr-Commit-Position: refs/heads/master@{#700335}

third_party/blink/renderer/core/accessibility/apply_dark_mode.cc

@@ -87,31 +87,19 @@ int GetBackgroundBrightnessThreshold(const Settings& frame_settings) {
              : frame_settings.GetDarkModeBackgroundBrightnessThreshold();
 }
 
-// A static wrapper to hold DarkModeSettings after initial creation.
-//
-// These settings are fixed after the browser launches, so they only need to be
-// constructed once for the "enabled" state and once for the "disabled" state.
-// Caching these values instead of re-calculating them should improve page load
-// performance.
-const DarkModeSettings& GetCachedEnabledSettings(
-    const Settings& frame_settings) {
-  static const DarkModeSettings* settings =
-      new DarkModeSettings([](const Settings& frame_settings) {
-        DarkModeSettings settings;
-        settings.mode = GetMode(frame_settings);
-        settings.image_policy = GetImagePolicy(frame_settings);
-        settings.text_brightness_threshold =
-            GetTextBrightnessThreshold(frame_settings);
-        settings.background_brightness_threshold =
-            GetBackgroundBrightnessThreshold(frame_settings);
-
-        settings.grayscale = frame_settings.GetDarkModeGrayscale();
-        settings.contrast = frame_settings.GetDarkModeContrast();
-        settings.image_grayscale_percent =
-            frame_settings.GetDarkModeImageGrayscale();
-        return settings;
-      }(frame_settings));
-  return *settings;
+DarkModeSettings GetEnabledSettings(const Settings& frame_settings) {
+  DarkModeSettings settings;
+  settings.mode = GetMode(frame_settings);
+  settings.image_policy = GetImagePolicy(frame_settings);
+  settings.text_brightness_threshold =
+      GetTextBrightnessThreshold(frame_settings);
+  settings.background_brightness_threshold =
+      GetBackgroundBrightnessThreshold(frame_settings);
+
+  settings.grayscale = frame_settings.GetDarkModeGrayscale();
+  settings.contrast = frame_settings.GetDarkModeContrast();
+  settings.image_grayscale_percent = frame_settings.GetDarkModeImageGrayscale();
+  return settings;
 }
 
 // In theory it should be sufficient for the disabled settings to set mode to
@@ -122,14 +110,11 @@ const DarkModeSettings& GetCachedEnabledSettings(
 //
 // TODO(gilmanmh): Investigate unexpected image inversion behavior when
 // image_policy not set to kFilterNone.
-const DarkModeSettings& GetCachedDisabledSettings() {
-  static const DarkModeSettings* settings = new DarkModeSettings([]() {
-    DarkModeSettings settings;
-    settings.mode = DarkModeInversionAlgorithm::kOff;
-    settings.image_policy = DarkModeImagePolicy::kFilterNone;
-    return settings;
-  }());
-  return *settings;
+DarkModeSettings GetDisabledSettings() {
+  DarkModeSettings settings;
+  settings.mode = DarkModeInversionAlgorithm::kOff;
+  settings.image_policy = DarkModeImagePolicy::kFilterNone;
+  return settings;
 }
 
 }  // namespace
@@ -139,9 +124,9 @@ DarkModeSettings BuildDarkModeSettings(const Settings& frame_settings,
   if (IsDarkModeEnabled(frame_settings) &&
       ShouldApplyDarkModeFilterToPage(frame_settings.GetDarkModePagePolicy(),
                                       root)) {
-    return GetCachedEnabledSettings(frame_settings);
+    return GetEnabledSettings(frame_settings);
   }
-  return GetCachedDisabledSettings();
+  return GetDisabledSettings();
 }
 
 bool ShouldApplyDarkModeFilterToPage(DarkModePagePolicy policy,