Adds field trial testing config for disabling zero-suggest caching

Canary experiment: cl/339288320
Beta experiment: cl/342939379

Bug: 1136654, 1136649
Change-Id: I447848638b80bf645de919b62ac14a5d499a55c5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2547920
Auto-Submit: Moe Ahmadi <mahmadi@chromium.org>
Commit-Queue: Ilya Sherman <isherman@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#829170}

testing/variations/fieldtrial_testing_config.json

@@ -4719,6 +4719,7 @@
                         "OmniboxDynamicMaxAutocomplete",
                         "OmniboxEntitySuggestionsReduceLatency",
                         "OmniboxLocalZeroSuggestAgeThreshold",
+                        "OmniboxLocalZeroSuggestForAuthenticatedUsers",
                         "OmniboxLocalZeroSuggestFrecencyRanking",
                         "OmniboxMaxURLMatches",
                         "OmniboxMaxZeroSuggestMatches",
@@ -4730,6 +4731,7 @@
                         "OmniboxRichEntitySuggestions",
                         "OmniboxTrendingZeroPrefixSuggestionsOnNTP",
                         "OmniboxUIExperimentMaxAutocompleteMatches",
+                        "OmniboxZeroSuggestCaching",
                         "QueryInOmnibox",
                         "SearchSuggestChips"
                     ]