[omnibox] Relocate On-Focus config in fieldtrial_testing_config.json

Currently, the on-focus configuration in fieldtrial_testing_config.json
is in the "NTPZeroPrefixSuggestions" trial.

The problem is that about_flags.cc configures on-focus suggestions with
the "OmniboxBundledExperimentV1" field trial. This mismatch between
fieldtrial_testing_config.json and about_flags.cc causes a crash.

It's most proper to match what's in fieldtrial_testing_config.json
and about_flags.cc.

We won't be able to match the server-side config all the time, since
Dev/Canary uses the "unbundled" experiment format, and Beta and Stable
use the "bundled" experiment format.

But so long as fieldtrial_testing_config.json and about_flags.cc match,
the client-side code is correct.

Bug: 1015174
Change-Id: I93fd6cf6392f3de2a0e326bbdfe736bb9a10acc2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2019329Reviewed-by: Moe Ahmadi <mahmadi@chromium.org>
Reviewed-by: Brian White <bcwhite@chromium.org>
Commit-Queue: Tommy Li <tommycli@chromium.org>
Cr-Commit-Position: refs/heads/master@{#736116}

testing/variations/fieldtrial_testing_config.json

@@ -3761,15 +3761,9 @@
             "experiments": [
                 {
                     "name": "Enabled",
-                    "params": {
-                        "ZeroSuggestVariant:15:*": "RemoteNoUrl,Local",
-                        "ZeroSuggestVariant:1:*": "RemoteNoUrl,Local",
-                        "ZeroSuggestVariant:7:*": "RemoteNoUrl,Local"
-                    },
                     "enable_features": [
                         "NtpRealbox",
                         "NtpRealboxMatchOmniboxTheme",
-                        "OmniboxOnFocusSuggestions",
                         "OmniboxSuggestionTransparencyOptions"
                     ]
                 }
@@ -4155,7 +4149,10 @@
                     "name": "DesktopExperiments",
                     "params": {
                         "OmniboxMaxURLMatches": "7",
-                        "UIMaxAutocompleteMatches": "8"
+                        "UIMaxAutocompleteMatches": "8",
+                        "ZeroSuggestVariant:15:*": "RemoteNoUrl,Local",
+                        "ZeroSuggestVariant:1:*": "RemoteNoUrl,Local",
+                        "ZeroSuggestVariant:7:*": "RemoteNoUrl,Local"
                     },
                     "enable_features": [
                         "OmniboxDisplayTitleForCurrentUrl",
@@ -4163,6 +4160,7 @@
                         "OmniboxEnableClipboardProviderTextSuggestions",
                         "OmniboxLocalEntitySuggestions",
                         "OmniboxMaxURLMatches",
+                        "OmniboxOnFocusSuggestions",
                         "OmniboxRemoveSuggestionsFromClipboard",
                         "OmniboxRichEntitySuggestions",
                         "OmniboxUIExperimentMaxAutocompleteMatches",