Adds places db cleanup in a background queue

Client/Application/UITestAppDelegate.swift

@@ -62,7 +62,7 @@ class UITestAppDelegate: AppDelegate, FeatureFlaggable {
                 try! FileManager.default.copyItem(at: input, to: output)
 
                 // Tests currently load a browserdb history, we make sure we migrate it everytime
-                UserDefaults.standard.setValue(false, forKey: PrefsKeys.HistoryMigratedToPlacesKey)
+                UserDefaults.standard.setValue(false, forKey: PrefsKeys.PlacesHistoryMigrationSucceeded)
             }
 
             if arg.starts(with: LaunchArguments.LoadTabsStateArchive) {

Providers/Profile.swift

@@ -536,11 +536,11 @@ open class BrowserProfile: Profile {
     }
 
     public func cleanupHistoryIfNeeded() {
-        // currently a no-op, but we should call
-        // places.runMaintenace here. At the time of writing this comment,
-        // it was run in Android once a day when the device is idle
-        // we should do something similar in iOS
-        // https://github.com/mozilla-mobile/firefox-ios/issues/12680
+        // We run the cleanup in the background, this is a low priority task
+        // that compacts the places db and reduces it's size to be under the limit.
+        DispatchQueue.global(qos: .background).async {
+            self.places.runMaintenance(dbSizeLimit: AppConstants.DB_SIZE_LIMIT_IN_BYTES)
+        }
     }
 
     public func sendQueuedSyncEvents() {

Shared/AppConstants.swift

@@ -114,4 +114,7 @@ public struct AppConstants {
 
     /// The maximum number of times we should attempt to migrated the History to Application Services Places DB
     public static let MAX_HISTORY_MIGRATION_ATTEMPT = 5
+
+    /// The maximum size of the places DB in bytes
+    public static let DB_SIZE_LIMIT_IN_BYTES: UInt32 = 75 * 1024 * 1024 // corresponds to 75MiB (in bytes)
 }