[omnibox] Adds field trial testing config for reactive zero-suggest

Beta finch config: cr/322802704

Change-Id: I626064d11e0a5d681db64111adad26aabf94dd95
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2353522
Commit-Queue: Moe Ahmadi <mahmadi@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#799183}

testing/variations/fieldtrial_testing_config.json

@@ -4540,6 +4540,8 @@
                         "OmniboxDocumentProvider",
                         "OmniboxMaxURLMatches",
                         "OmniboxMaxZeroSuggestMatches",
+                        "OmniboxReactiveZeroSuggestionsOnNTPOmnibox",
+                        "OmniboxReactiveZeroSuggestionsOnNTPRealbox",
                         "OmniboxRemoveSuggestionsFromClipboard",
                         "OmniboxRichEntitySuggestions",
                         "OmniboxUIExperimentMaxAutocompleteMatches",