Chrome New Tab Page: start adding a "real" search box ("realbox")

This CL simply adds a feature ([k]NtpRealbox).

This is for a11y purposes and to fix the [currently somewhat broken]
NTP fullscreen experience, and to allow on-focus suggestions.

R=mahmadi@chromium.org
BUG=243926, 778489, 996516

Change-Id: Ic7347be02391290dfc6214a1754558e91b6c7802
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1769035
Auto-Submit: Dan Beam <dbeam@chromium.org>
Commit-Queue: Moe Ahmadi <mahmadi@chromium.org>
Reviewed-by: Moe Ahmadi <mahmadi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#690397}

chrome/browser/search/ntp_features.cc

@@ -35,4 +35,10 @@ const base::Feature kNtpCustomizationMenuV2{"NtpCustomizationMenuV2",
 const base::Feature kFirstRunDefaultSearchShortcut{
     "FirstRunDefaultSearchShortcut", base::FEATURE_DISABLED_BY_DEFAULT};
 
+// If enabled, the search box in the middle of the NTP will accept input
+// directly (i.e. not be a "fake" box) and search results will show directly
+// below the non-fake input ("realbox").
+const base::Feature kNtpRealbox{"NtpRealbox",
+                                base::FEATURE_DISABLED_BY_DEFAULT};
+
 }  // namespace features

chrome/browser/search/ntp_features.h

@@ -20,6 +20,8 @@ extern const base::Feature kNtpCustomizationMenuV2;
 
 extern const base::Feature kFirstRunDefaultSearchShortcut;
 
+extern const base::Feature kNtpRealbox;
+
 }  // namespace features
 
 #endif  // CHROME_BROWSER_SEARCH_NTP_FEATURES_H_