WebContent+WebDriver: Fully implement closing a session

There were a couple steps missing to close the remote end. Further, we
were not removing the session from the list of active sessions.

Userland/Services/WebContent/WebDriverClient.ipc

@@ -1,6 +1,7 @@
 #include <LibWeb/WebDriver/Response.h>
 
 endpoint WebDriverClient {
+    close_session() => ()
     set_is_webdriver_active(bool active) =|
     navigate_to(JsonValue payload) => (Web::WebDriver::Response response)
     get_current_url() => (Web::WebDriver::Response response)

Userland/Services/WebContent/WebDriverConnection.cpp

@@ -50,6 +50,16 @@ WebDriverConnection::WebDriverConnection(NonnullOwnPtr<Core::Stream::LocalSocket
 {
 }
 
+// https://w3c.github.io/webdriver/#dfn-close-the-session
+void WebDriverConnection::close_session()
+{
+    // 1. Set the webdriver-active flag to false.
+    set_is_webdriver_active(false);
+
+    // 2. An endpoint node must close any top-level browsing contexts associated with the session, without prompting to unload.
+    m_page_host.page().top_level_browsing_context().close();
+}
+
 void WebDriverConnection::set_is_webdriver_active(bool is_webdriver_active)
 {
     m_page_host.set_is_webdriver_active(is_webdriver_active);

Userland/Services/WebContent/WebDriverConnection.h

@@ -28,6 +28,8 @@ private:
     WebDriverConnection(NonnullOwnPtr<Core::Stream::LocalSocket> socket, PageHost& page_host);
 
     virtual void die() override { }
+
+    virtual void close_session() override;
     virtual void set_is_webdriver_active(bool) override;
     virtual Messages::WebDriverClient::NavigateToResponse navigate_to(JsonValue const& payload) override;
     virtual Messages::WebDriverClient::GetCurrentUrlResponse get_current_url() override;