[omnibox] Adds field trial testing config for increased # of zero-suggest

Beta finch config: cr/326309353

Change-Id: I9e014c50e6fadbd5dd6ccd55e99087c9530965ec
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2351500
Commit-Queue: Moe Ahmadi <mahmadi@chromium.org>
Reviewed-by: Mark Pearson <mpearson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#798417}

testing/variations/fieldtrial_testing_config.json

@@ -4889,6 +4889,7 @@
                 {
                     "name": "DesktopExperiments",
                     "params": {
+                        "MaxZeroSuggestMatches": "10",
                         "OmniboxMaxURLMatches": "7",
                         "UIMaxAutocompleteMatches": "8"
                     },
@@ -4896,6 +4897,7 @@
                         "OmniboxDisplayTitleForCurrentUrl",
                         "OmniboxDocumentProvider",
                         "OmniboxMaxURLMatches",
+                        "OmniboxMaxZeroSuggestMatches",
                         "OmniboxRemoveSuggestionsFromClipboard",
                         "OmniboxRichEntitySuggestions",
                         "OmniboxUIExperimentMaxAutocompleteMatches",