[Start Surface] Intercept click events on tabswitcher toolbar.

Clicks on the toolbar are currently passed through the url_bar behind it.
This leads to unexpected behavior when not user-visible views handle click events.
The change makes the toolbar intercept all click events on not user-visible views.

Accessibility is unaffected, see here: https://drive.google.com/file/d/1LDGfFfaCkg2meUNPX3211HE2_bIJGJNr/view?usp=sharing

Bug: 982018
Change-Id: Ibadba84a8f500cb7cf7aaa5129c91b11f2a5e9e0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1887150Reviewed-by: Yusuf Ozuysal <yusufo@chromium.org>
Reviewed-by: Ganggui Tang <gogerald@chromium.org>
Commit-Queue: Mia Glaese <glamia@chromium.org>
Cr-Commit-Position: refs/heads/master@{#710894}

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

@@ -8,7 +8,8 @@
     xmlns:app="http://schemas.android.com/apk/res-auto"
     android:id="@+id/tab_switcher_toolbar"
     android:layout_width="match_parent"
-    android:layout_height="@dimen/toolbar_height_no_shadow" >
+    android:layout_height="@dimen/toolbar_height_no_shadow"
+    android:clickable="true" >
 
     <LinearLayout
         android:layout_width="wrap_content"