Missing smooth scroll effect on history traversal

The cause of this bug is that the default Scroll Behavior during history traversal is instant scroll. Changing it to auto fixes the issue.

Bug: 830971
Change-Id: I1c29669b0b630a3d7f6d778892215a91763f2a97
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2085700Reviewed-by: David Bokan <bokan@chromium.org>
Commit-Queue: Liviu Tinta <liviutinta@chromium.org>
Cr-Commit-Position: refs/heads/master@{#747304}

third_party/blink/renderer/core/paint/paint_layer_scrollable_area.cc

@@ -245,7 +245,8 @@ void PaintLayerScrollableArea::ApplyPendingHistoryRestoreScrollOffset() {
        pending_view_state_->scroll_anchor_data_.simhash_});
   if (!did_restore) {
     SetScrollOffset(pending_view_state_->scroll_offset_,
-                    mojom::blink::ScrollType::kProgrammatic);
+                    mojom::blink::ScrollType::kProgrammatic,
+                    mojom::blink::ScrollBehavior::kAuto);
   }
 
   pending_view_state_.reset();