Fix downloads controller crash

Bug: 1021318
Change-Id: I98b7163f149a82f737f04ede5fd2817c6bb3108d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1900091Reviewed-by: Shakti Sahu <shaktisahu@chromium.org>
Commit-Queue: Matthew Jones <mdjones@chromium.org>
Auto-Submit: Matthew Jones <mdjones@chromium.org>
Cr-Commit-Position: refs/heads/master@{#712782}

chrome/android/java/src/org/chromium/chrome/browser/download/DownloadInfoBarController.java

@@ -371,7 +371,10 @@ public class DownloadInfoBarController implements OfflineContentProvider.Observe
     public IPHInfoBarSupport.TrackerParameters getTrackerParameters() {
         if (getDownloadCount().inProgress == 0) return null;
 
-        if (getCurrentTab().getActivity().getBottomSheetController().isSheetOpen()) return null;
+        if (getCurrentTab() == null || getCurrentTab().getActivity() == null
+                || getCurrentTab().getActivity().getBottomSheetController().isSheetOpen()) {
+            return null;
+        }
 
         return new IPHInfoBarSupport.TrackerParameters(
                 FeatureConstants.DOWNLOAD_INFOBAR_DOWNLOADS_ARE_FASTER_FEATURE,