Tab Search: Scroll animation bug fix

Fix scroll bug on repeated quick press of up/down keys on first/last
selector entries.

Fixed: 1110505
Change-Id: I84c015cfd21c6b8c8dd477dcd327ef23e09012ae
Reviewed-on: https://chrome-internal-review.googlesource.com/c/chrome/browser/resources/tab_search/+/3201593Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Reviewed-by: Tom Lukaszewicz <tluk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#819576}

chrome/browser/resources/tab_search_merge/app.js

@@ -188,14 +188,16 @@ export class TabSearchAppElement extends PolymerElement {
     // Ensure the scroll view can fully display a preceding or following tab
     // item if existing. Use Math.sign to identify any such preceding or
     // following item.
-    const scrollToIndex =
-        (this.selectedIndex_ === 0 ||
-         this.selectedIndex_ === this.filteredOpenTabs_.length - 1) ?
-        this.selectedIndex_ :
-        this.selectedIndex_ + Math.sign(offset);
-
-    this.getTabSearchItem_(scrollToIndex)
-        .scrollIntoView({behavior: 'smooth', block: 'nearest'});
+    if (this.selectedIndex_ === 0 ||
+        this.selectedIndex_ === this.filteredOpenTabs_.length - 1) {
+      this.getTabSearchItem_(this.selectedIndex_).scrollIntoView({
+        behavior: 'smooth'
+      });
+    } else {
+      this.getTabSearchItem_(this.selectedIndex_ + Math.sign(offset))
+          .scrollIntoView(
+              {behavior: 'smooth', block: offset > 0 ? 'end' : 'start'});
+    }
   }
 }