[Omnibox] Adds flag to enable search suggest chips to fieldtrial config

zero-prefix suggestions disabled search suggest chips. In order to
better understand the impact of search suggest chips on realbox
performance SearchSuggestChips feature will be used in the latest realbox
experiments in M83. This feature has been tested on Canary as part of
NtpRealboxZeroPrefixSuggestionsDesktop study

Change-Id: Id8f2f0e69da06af5203dc842c66dd01d6d5bfb7d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2218723Reviewed-by: Mark Pearson <mpearson@chromium.org>
Commit-Queue: Moe Ahmadi <mahmadi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#772566}

testing/variations/fieldtrial_testing_config.json

@@ -3893,7 +3893,8 @@
                         "OmniboxRichEntitySuggestions",
                         "OmniboxUIExperimentMaxAutocompleteMatches",
                         "OmniboxZeroSuggestionsOnNTP",
-                        "QueryInOmnibox"
+                        "QueryInOmnibox",
+                        "SearchSuggestChips"
                     ]
                 }
             ]