Browser: Go back/forward when pressing back/forward mouse buttons

This currently doesn't work when running Serenity through QEMU, as it
doesn't pass the side button events over to Serenity due to some bug or
missing feature.

Author: Baitinq

Userland/Applications/Browser/Tab.cpp

@@ -445,6 +445,16 @@ Tab::Tab(BrowserWindow& window)
         load(url);
     };
 
+    view().on_back_button = [this] {
+        if (m_history.can_go_back())
+            go_back();
+    };
+
+    view().on_forward_button = [this] {
+        if (m_history.can_go_forward())
+            go_forward();
+    };
+
     m_tab_context_menu = GUI::Menu::construct();
     m_tab_context_menu->add_action(GUI::CommonActions::make_reload_action([this](auto&) {
         reload();

Userland/Libraries/LibWebView/OutOfProcessWebView.cpp

@@ -174,6 +174,12 @@ void OutOfProcessWebView::mousedown_event(GUI::MouseEvent& event)
 void OutOfProcessWebView::mouseup_event(GUI::MouseEvent& event)
 {
     enqueue_input_event(event);
+
+    if (event.button() == GUI::MouseButton::Backward && on_back_button) {
+        on_back_button();
+    } else if (event.button() == GUI::MouseButton::Forward && on_forward_button) {
+        on_forward_button();
+    }
 }
 
 void OutOfProcessWebView::mousemove_event(GUI::MouseEvent& event)

Userland/Libraries/LibWebView/OutOfProcessWebView.h

@@ -111,6 +111,8 @@ class OutOfProcessWebView final
     Function<Gfx::IntRect()> on_maximize_window;
     Function<Gfx::IntRect()> on_minimize_window;
     Function<Gfx::IntRect()> on_fullscreen_window;
+    Function<void()> on_back_button;
+    Function<void()> on_forward_button;
 
 private:
     OutOfProcessWebView();