LibWeb: Defer the handling of WebContent process crashes

Handling crashes synchronously is finicky since we're modifying the
m_client_state struct while in a callback lambda owned by it.
Let's avoid all the footguns here by simply using deferred_invoke()
and handling the crash on next event loop iteration instead.

Userland/Libraries/LibWeb/OutOfProcessWebView.cpp

@@ -52,12 +52,8 @@ OutOfProcessWebView::~OutOfProcessWebView()
 {
 }
 
-void OutOfProcessWebView::create_client()
+void OutOfProcessWebView::handle_web_content_process_crash()
 {
-    m_client_state = {};
-
-    m_client_state.client = WebContentClient::construct(*this);
-    m_client_state.client->on_web_content_process_crash = [this] {
     create_client();
     ASSERT(m_client_state.client);
 
@@ -77,6 +73,17 @@ void OutOfProcessWebView::create_client()
     builder.appendff("The web page <a href=\"{}\">{}</a> has crashed.<br><br>You can reload the page to try again.", escape_html_entities(m_url.to_string_encoded()), escape_html_entities(m_url.to_string()));
     builder.append("</body></html>");
     load_html(builder.to_string(), m_url);
+}
+
+void OutOfProcessWebView::create_client()
+{
+    m_client_state = {};
+
+    m_client_state.client = WebContentClient::construct(*this);
+    m_client_state.client->on_web_content_process_crash = [this] {
+        deferred_invoke([this] {
+            handle_web_content_process_crash();
+        });
     };
 
     client().post_message(Messages::WebContentServer::UpdateSystemTheme(Gfx::current_system_theme_buffer()));

Userland/Libraries/LibWeb/OutOfProcessWebView.h

@@ -90,6 +90,8 @@ private:
     void create_client();
     WebContentClient& client();
 
+    void handle_web_content_process_crash();
+
     URL m_url;
 
     struct ClientState {