Make tab switcher bottom toolbar clickable

Make tab switcher bottom toolbar clickable to prevent clicks from
going through the bottom bar and selecting a tab.

Bug: 905077
Change-Id: Iae34cd43f6f82aef1c8d62cdcdad20e38b075d5b
Reviewed-on: https://chromium-review.googlesource.com/c/1351753Reviewed-by: Matthew Jones <mdjones@chromium.org>
Commit-Queue: Pedro Amaral <amaralp@chromium.org>
Cr-Commit-Position: refs/heads/master@{#611273}

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

@@ -9,7 +9,8 @@
     android:id="@+id/bottom_toolbar_tab_switcher"
     android:layout_width="match_parent"
     android:layout_height="wrap_content"
-    android:visibility="gone" >
+    android:visibility="gone"
+    android:clickable="true" >
 
     <ImageView
         android:id="@+id/bottom_toolbar_top_shadow"