[Duet] Add touch highlight to new tab button

BUG=1036471

Change-Id: Ia387b4a5cba67581d8607016ee05df403310c864
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2017103
Auto-Submit: Theresa  <twellington@chromium.org>
Commit-Queue: Sinan Sahin <sinansahin@google.com>
Reviewed-by: Sinan Sahin <sinansahin@google.com>
Cr-Commit-Position: refs/heads/master@{#735056}

chrome/android/java/res/layout/bottom_toolbar_browsing.xml

@@ -30,6 +30,7 @@
         android:id="@+id/bottom_new_tab_button"
         android:contentDescription="@string/accessibility_toolbar_btn_new_tab"
         app:tint="@color/standard_mode_tint"
+        android:background="?attr/selectableItemBackgroundBorderless"
         app:srcCompat="@drawable/new_tab_icon"
         android:visibility="gone"
         style="@style/SplitToolbarButton" />