Don't return false to cancel drawing when destroying FeedSliceViewTracker

This fixes the drawinf freezing problem when the user navigates away
from Feed v2 page.

Bug: none
Change-Id: I2d14aa6eac0f03ff51c561ae34a65cdc011d664c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2242200Reviewed-by: Dan H <harringtond@chromium.org>
Commit-Queue: Jian Li <jianli@chromium.org>
Cr-Commit-Position: refs/heads/master@{#777539}

chrome/android/feed/core/java/src/org/chromium/chrome/browser/feed/v2/FeedSliceViewTracker.java

@@ -60,7 +60,7 @@ class FeedSliceViewTracker implements ViewTreeObserver.OnPreDrawListener {
     @Override
     public boolean onPreDraw() {
         // Not sure why, but this method can be called just after destroy().
-        if (mRootView == null) return false;
+        if (mRootView == null) return true;
         if (!(mRootView.getLayoutManager() instanceof LinearLayoutManager)) return true;
 
         LinearLayoutManager layoutManager = (LinearLayoutManager) mRootView.getLayoutManager();