[New Tab Page] Don't record metrics if page destroyed

It removes a minor inconsistency across UMA metrics, since some are
recorded always (code before early return), and others depending on
mIsDestroyed (below after early return).

It shouldn't make a big difference in practice due to how unlikely the
scenario is: the New Tab Page is closed while it is in the process of
loading (including icons, etc.).

BUG=

Review-Url: https://codereview.chromium.org/1965543005
Cr-Commit-Position: refs/heads/master@{#392892}

chrome/android/java/src/org/chromium/chrome/browser/ntp/NewTabPage.java

@@ -525,16 +525,17 @@ public void onLogoAvailable(Logo logo, boolean fromCache) {
 
         @Override
         public void onLoadingComplete(MostVisitedItem[] items) {
+            if (mIsDestroyed) return;
+
             long loadTimeMs = (System.nanoTime() - mConstructedTimeNs) / 1000000;
             RecordHistogram.recordTimesHistogram(
                     "Tab.NewTabOnload", loadTimeMs, TimeUnit.MILLISECONDS);
             mIsLoaded = true;
+            // TODO(mastiz): revisit the logic for mIsLoaded and mIsVisible, since setting
+            // mIsVisible to true seems wrong here.
             mIsVisible = true;
             StartupMetrics.getInstance().recordOpenedNTP();
             NewTabPageUma.recordNTPImpression(NewTabPageUma.NTP_IMPRESSION_REGULAR);
-
-            if (mIsDestroyed) return;
-
             recordNTPShown();
 
             int tileTypes[] = new int[items.length];