Add dark search feature flag

Shows the darkened search screen when the user's device is in night
mode.

design doc: go/clank-dark-search

Bug: 1079074
Change-Id: I56632a6e579db488c2be2e9c5e7eeee47eb62989
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2186128
Reviewed-by: Brian White <[email protected]>
Reviewed-by: Theresa  <[email protected]>
Reviewed-by: Filip Gorski <[email protected]>
Commit-Queue: Brandon Wylie <[email protected]>
Cr-Commit-Position: refs/heads/master@{#768470}
diff --git a/chrome/browser/about_flags.cc b/chrome/browser/about_flags.cc
index 3a12b4b..9fbbb77 100644
--- a/chrome/browser/about_flags.cc
+++ b/chrome/browser/about_flags.cc
@@ -2990,6 +2990,10 @@
                                     "ForceDarkVariations")},
 #endif  // !OS_CHROMEOS
 #if defined(OS_ANDROID)
+    {"enable-android-dark-search", flag_descriptions::kAndroidDarkSearchName,
+     flag_descriptions::kAndroidDarkSearchDescription, kOsAndroid,
+     FEATURE_VALUE_TYPE(features::kAndroidDarkSearch)},
+
     {"enable-android-night-mode-tab-reparenting",
      flag_descriptions::kAndroidNightModeTabReparentingName,
      flag_descriptions::kAndroidNightModeTabReparentingDescription, kOsAndroid,