Add "OmniboxOnFocusSuggestionsContextualWebOnContent" flag to fieldtrial testing.

Bug: 1087700
Change-Id: I05d6c896298e2094834f9e14f2e517a3009a7a47
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2419411Reviewed-by: Steven Holte <holte@chromium.org>
Commit-Queue: Steven Holte <holte@chromium.org>
Auto-Submit: Tomasz Wiszkowski <ender@google.com>
Cr-Commit-Position: refs/heads/master@{#809140}

testing/variations/fieldtrial_testing_config.json

@@ -4872,6 +4872,7 @@
                         "OmniboxCompactSuggestions",
                         "OmniboxMaxURLMatches",
                         "OmniboxMaxZeroSuggestMatches",
+                        "OmniboxOnFocusSuggestionsContextualWebOnContent",
                         "OmniboxUIExperimentMaxAutocompleteMatches"
                     ]
                 }