Omnibox UI Experiments: Vert. margin and title-swap in testing config.

Turns on these Omnibox UI experiments in the fieldtrial testing config:
 - Swap title and URL
 - Vertical margin 8px

Bug: 794203, 794204
Change-Id: I4f5c29ae845e38d42a5d8a1145e1d64bdb92542b
Reviewed-on: https://chromium-review.googlesource.com/891632Reviewed-by: Mark Pearson <mpearson@chromium.org>
Commit-Queue: Tommy Li <tommycli@chromium.org>
Cr-Commit-Position: refs/heads/master@{#533147}

testing/variations/fieldtrial_testing_config.json

@@ -2352,10 +2352,15 @@
             ],
             "experiments": [
                 {
-                    "name": "HideSuggestionUrlSchemeAndTrivialSubdomains",
+                    "name": "UIExperiments",
+                    "params": {
+                        "UIVerticalMargin": "8"
+                    },
                     "enable_features": [
                         "OmniboxUIExperimentHideSuggestionUrlScheme",
-                        "OmniboxUIExperimentHideSuggestionUrlTrivialSubdomains"
+                        "OmniboxUIExperimentHideSuggestionUrlTrivialSubdomains",
+                        "OmniboxUIExperimentSwapTitleAndUrl",
+                        "OmniboxUIExperimentVerticalMargin"
                     ]
                 }
             ]