[Assistant Voice Search] Setup feature flag

Just the feature flag and related setup for now, I'll follow-up with the
functionality in another CL.

Bug: 1041576
PRD: go/roti-prd
Doc: go/roti-chrome-design
Change-Id: I51b65fe999c9679201ca28ef8e88eeee9966fef2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1997652
Commit-Queue: Brandon Wylie <[email protected]>
Reviewed-by: Tommy Li <[email protected]>
Reviewed-by: Brian White <[email protected]>
Reviewed-by: Patrick Noland <[email protected]>
Reviewed-by: Ender <[email protected]>
Cr-Commit-Position: refs/heads/master@{#734315}
diff --git a/chrome/browser/flag_descriptions.h b/chrome/browser/flag_descriptions.h
index 05a2645..5112a3e 100644
--- a/chrome/browser/flag_descriptions.h
+++ b/chrome/browser/flag_descriptions.h
@@ -847,6 +847,9 @@
 extern const char kOfferStoreUnmaskedWalletCardsName[];
 extern const char kOfferStoreUnmaskedWalletCardsDescription[];
 
+extern const char kOmniboxAssistantVoiceSearchName[];
+extern const char kOmniboxAssistantVoiceSearchDescription[];
+
 extern const char kOmniboxAutocompleteTitlesName[];
 extern const char kOmniboxAutocompleteTitlesDescription[];