LibGUI: Make FilePicker's common location buttons checkable

We now use the checked state of these buttons to indicate that you are
in that specific folder. The checked state is updated automagically
no matter how you navigate the file system. :^)

Userland/Libraries/LibGUI/FilePicker.cpp

@@ -120,8 +120,6 @@ FilePicker::FilePicker(Window* parent_window, Mode mode, const StringView& file_
     m_view->set_column_visible(FileSystemModel::Column::Inode, true);
     m_view->set_column_visible(FileSystemModel::Column::SymlinkTarget, true);
 
-    set_path(path);
-
     m_model->register_client(*this);
 
     m_location_textbox->on_return_pressed = [this] {
@@ -225,20 +223,39 @@ FilePicker::FilePicker(Window* parent_window, Mode mode, const StringView& file_
     };
 
     auto& common_locations_frame = *widget.find_descendant_of_type_named<GUI::Frame>("common_locations_frame");
-    auto add_common_location_button = [&](auto& name, String path) {
+    auto add_common_location_button = [&](auto& name, String path) -> GUI::Button& {
         auto& button = common_locations_frame.add<GUI::Button>();
         button.set_button_style(Gfx::ButtonStyle::CoolBar);
         button.set_text_alignment(Gfx::TextAlignment::CenterLeft);
         button.set_text(move(name));
         button.set_icon(FileIconProvider::icon_for_path(path).bitmap_for_size(16));
         button.set_fixed_height(22);
+        button.set_checkable(true);
+        button.set_exclusive(true);
         button.on_click = [this, path] {
             set_path(path);
         };
+        return button;
     };
-    add_common_location_button("Home", Core::StandardPaths::home_directory());
-    add_common_location_button("Desktop", Core::StandardPaths::desktop_directory());
-    add_common_location_button("Root", "/");
+    auto& home_button = add_common_location_button("Home", Core::StandardPaths::home_directory());
+    auto& desktop_button = add_common_location_button("Desktop", Core::StandardPaths::desktop_directory());
+    auto& root_button = add_common_location_button("Root", "/");
+
+    m_model->on_complete = [&] {
+        if (m_model->root_path() == Core::StandardPaths::home_directory()) {
+            home_button.set_checked(true);
+        } else if (m_model->root_path() == Core::StandardPaths::desktop_directory()) {
+            desktop_button.set_checked(true);
+        } else if (m_model->root_path() == "/") {
+            root_button.set_checked(true);
+        } else {
+            home_button.set_checked(false);
+            desktop_button.set_checked(false);
+            root_button.set_checked(false);
+        }
+    };
+
+    set_path(path);
 }
 
 FilePicker::~FilePicker()

Userland/Libraries/LibGUI/FilePickerDialog.gml

@@ -20,7 +20,7 @@
 
         @GUI::Frame {
             name: "common_locations_frame"
-            fixed_width: 80
+            fixed_width: 90
             fill_with_background_color: true
 
             layout: @GUI::VerticalBoxLayout {