[Paint Preview] Only show upgrade toast when tab is visible

Bug: 1138902
Change-Id: If0a8944718004ab56f7e60c532b051ded909ea0b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2476033
Commit-Queue: Mehran Mahmoudi <mahmoudi@chromium.org>
Commit-Queue: Calder Kitagawa <ckitagawa@chromium.org>
Auto-Submit: Mehran Mahmoudi <mahmoudi@chromium.org>
Reviewed-by: Calder Kitagawa <ckitagawa@chromium.org>
Cr-Commit-Position: refs/heads/master@{#817510}

chrome/browser/paint_preview/android/java/src/org/chromium/chrome/browser/paint_preview/StartupPaintPreview.java

@@ -144,7 +144,7 @@ public class StartupPaintPreview implements PlayerManager.Listener {
     }
 
     private void showUpgradeToast() {
-        if (mTab == null) return;
+        if (mTab == null || mTab.isHidden()) return;
 
         Toast.makeText(mTab.getContext(), R.string.paint_preview_startup_auto_upgrade_toast,
                      Toast.LENGTH_SHORT)