Browser: Add a banner to tabs controlled by WebDriver

From https://www.w3.org/TR/webdriver/#security:

It is also suggested that user agents make an effort to visually
distinguish a user agent session that is under control of WebDriver from
those used for normal browsing sessions. This can be done through a
browser chrome element such as a “door hanger”, colorful decoration of
the OS window, or some widget element that is prevalent in the window so
that it easy to identify automation windows.

Author: linusg

Userland/Applications/Browser/Tab.cpp

@@ -668,6 +668,8 @@ void Tab::hide_event(GUI::HideEvent&)
 void Tab::enable_webdriver_mode()
 {
     m_web_content_view->set_is_webdriver_active(true);
+    auto& webdriver_banner = *find_descendant_of_type_named<GUI::Widget>("webdriver_banner");
+    webdriver_banner.set_visible(true);
 }
 
 }

Userland/Applications/Browser/Tab.gml

@@ -11,6 +11,26 @@
         }
     }
 
+    @GUI::Frame {
+        name: "webdriver_banner"
+        shape: "Box"
+        shadow: "Sunken"
+        thickness: 1
+        preferred_height: "shrink"
+        foreground_role: "TooltipText"
+        background_role: "Tooltip"
+        fill_with_background_color: true
+        visible: false
+        layout: @GUI::HorizontalBoxLayout {
+            margins: [0, 4]
+        }
+
+        @GUI::Label {
+            text: "This Browser window is controlled by WebDriver."
+            text_alignment: "CenterLeft"
+        }
+    }
+
     @GUI::Widget {
         name: "webview_container"
         layout: @GUI::VerticalBoxLayout {}