Add omnibox feature flag for context menu show full URLs

UX proposal: https://docs.google.com/document/d/19iu3ISlOw9L_PCpOh8LB4TSKC8uBPzSBiEnkZm4IiQI/edit#heading=h.qyrxas7ncbc9
Design doc: go/context-menu-unelide-dd

Bug: 1061576
Change-Id: I3627f0090112378f6df8bbaf274b40c35024a7c6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2103291
Commit-Queue: Livvie Lin <[email protected]>
Reviewed-by: Tommy Li <[email protected]>
Cr-Commit-Position: refs/heads/master@{#751066}
diff --git a/components/omnibox/common/omnibox_features.h b/components/omnibox/common/omnibox_features.h
index 0f150cd..35c9a96 100644
--- a/components/omnibox/common/omnibox_features.h
+++ b/components/omnibox/common/omnibox_features.h
@@ -74,6 +74,7 @@
 // Omnibox UI - these affect the UI or function of the location bar (not the
 // popup).
 extern const base::Feature kOmniboxAssistantVoiceSearch;
+extern const base::Feature kOmniboxContextMenuShowFullUrls;
 
 }  // namespace omnibox