Add browsertests for tab sharing UI views.

Add tests to verify tab sharing UI elements: infobars, contents border
and tab sharing indicator.

Bug: 996722
Change-Id: I5fa5ec7e4a48a66c1ba9b08ff76b84a105961352
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1847287Reviewed-by: Guido Urdaneta <guidou@chromium.org>
Commit-Queue: Marina Ciocea <marinaciocea@chromium.org>
Cr-Commit-Position: refs/heads/master@{#707368}

chrome/test/BUILD.gn

@@ -5642,6 +5642,7 @@ if (!is_android) {
         "../browser/ui/views/passwords/password_bubble_interactive_uitest.cc",
         "../browser/ui/views/sad_tab_view_interactive_uitest.cc",
         "../browser/ui/views/status_icons/status_tray_state_changer_interactive_uitest_win.cc",
+        "../browser/ui/views/tab_sharing/tab_sharing_ui_views_browsertest.cc",
         "../browser/ui/views/tabs/tab_drag_controller_interactive_uitest.cc",
         "../browser/ui/views/tabs/tab_drag_controller_interactive_uitest.h",
         "../browser/ui/views/tabs/tab_hover_card_bubble_view_interactive_uitest.cc",