Change priority of task to record Servicification.Startup3 to DEFAULT.

BEST_EFFORT does not work in background (crbug.com/988604).

Bug: 988604, 984559
Change-Id: I99f3793d9bb949570cd78c9f969b05fea138aed7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1726870
Commit-Queue: Henrique Nakashima <hnakashima@chromium.org>
Commit-Queue: Mohamed Heikal <mheikal@chromium.org>
Reviewed-by: Mohamed Heikal <mheikal@chromium.org>
Cr-Commit-Position: refs/heads/master@{#682426}

chrome/android/java/src/org/chromium/chrome/browser/init/ChromeBrowserInitializer.java

@@ -318,7 +318,7 @@ public class ChromeBrowserInitializer {
 
         int startupMode =
                 getBrowserStartupController().getStartupMode(delegate.startServiceManagerOnly());
-        tasks.add(UiThreadTaskTraits.BEST_EFFORT,
+        tasks.add(UiThreadTaskTraits.DEFAULT,
                 () -> { BackgroundTaskSchedulerExternalUma.reportStartupMode(startupMode); });
 
         if (isAsync) {