[omnibox] Add official flag for experimental keyword mode

Simply adds a flag for the existing feature.

Bug: 883901
Change-Id: I13076b469f55f14ef0cc52f573fc2648736c6684
Reviewed-on: https://chromium-review.googlesource.com/c/1440183
Reviewed-by: Avi Drissman <[email protected]>
Reviewed-by: manuk hovanesian <[email protected]>
Commit-Queue: Kevin Bailey <[email protected]>
Cr-Commit-Position: refs/heads/master@{#628126}
diff --git a/chrome/browser/flag_descriptions.h b/chrome/browser/flag_descriptions.h
index d21bc7b..f6f2995 100644
--- a/chrome/browser/flag_descriptions.h
+++ b/chrome/browser/flag_descriptions.h
@@ -1681,6 +1681,9 @@
 extern const char kOmniboxDriveSuggestionsName[];
 extern const char kOmniboxDriveSuggestionsDescriptions[];
 
+extern const char kOmniboxExperimentalKeywordModeName[];
+extern const char kOmniboxExperimentalKeywordModeDescription[];
+
 extern const char kOmniboxPedalSuggestionsName[];
 extern const char kOmniboxPedalSuggestionsDescription[];