[NTP][RQ] Adds field trial testing config for repeatable queries

This is in preparation to promote the canary experiment which
originally landed in cl/339288320 to Beta.

Fixed: 1155314
Change-Id: I4b87b89736e4cb461d416aacef98ed888596568c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2573130
Commit-Queue: Moe Ahmadi <mahmadi@chromium.org>
Reviewed-by: Weilun Shi <sweilun@chromium.org>
Cr-Commit-Position: refs/heads/master@{#833576}

components/ntp_tiles/most_visited_sites.cc

@@ -401,10 +401,9 @@ void MostVisitedSites::AddOrRemoveBlockedUrl(const GURL& url, bool add_url) {
   }
 
   if (repeatable_queries_) {
+    // Restoring repeatable queries is not supported as deletion is permanent.
     if (add_url)
       repeatable_queries_->DeleteQueryWithDestinationURL(url);
-    else
-      NOTREACHED() << "Deleted repeatable queries cannot be restored.";
   }
 
   if (top_sites_) {

testing/variations/fieldtrial_testing_config.json

@@ -4632,6 +4632,30 @@
             ]
         }
     ],
+    "NtpRepeatableQueriesDesktop": [
+        {
+            "platforms": [
+                "chromeos",
+                "linux",
+                "mac",
+                "windows"
+            ],
+            "experiments": [
+                {
+                    "name": "Enabled",
+                    "params": {
+                        "NtpRepeatableQueriesAgeThresholdDays": "180",
+                        "NtpRepeatableQueriesFrequencyExponent": "2",
+                        "NtpRepeatableQueriesInsertPosition": "start",
+                        "NtpRepeatableQueriesRecencyHalfLifeSeconds": "604800"
+                    },
+                    "enable_features": [
+                        "NtpRepeatableQueries"
+                    ]
+                }
+            ]
+        }
+    ],
     "NtpWebUIDesktop": [
         {
             "platforms": [