Add field trial testing config for frecency ranking of local history ZPS

Canary experiment: cr/329566898

Bug: 1096615
Change-Id: I8d75aec33c254d3aabe8ca8efae360c60e44a3d9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2431462
Commit-Queue: Moe Ahmadi <mahmadi@chromium.org>
Commit-Queue: Mark Pearson <mpearson@chromium.org>
Auto-Submit: Moe Ahmadi <mahmadi@chromium.org>
Reviewed-by: Mark Pearson <mpearson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#810864}

testing/variations/fieldtrial_testing_config.json

@@ -4730,11 +4730,14 @@
                     "name": "DesktopExperiments",
                     "params": {
                         "MaxZeroSuggestMatches": "10",
+                        "OmniboxLocalZeroSuggestAgeThreshold": "7",
                         "OmniboxMaxURLMatches": "7",
                         "UIMaxAutocompleteMatches": "8"
                     },
                     "enable_features": [
                         "OmniboxDisplayTitleForCurrentUrl",
+                        "OmniboxLocalZeroSuggestAgeThreshold",
+                        "OmniboxLocalZeroSuggestFrecencyRanking",
                         "OmniboxMaxURLMatches",
                         "OmniboxMaxZeroSuggestMatches",
                         "OmniboxReactiveZeroSuggestionsOnNTPOmnibox",