ProfileViewer: Begin work on a visualization tool for profiles :^)

We begin with a simple treeview that shows a recorded profile.
To record and view a profile of a process with <PID>, simply do this:

$ profile <PID> on
... wait while PID does something interesting ...
$ profile <PID> off
$ cat /proc/profile > my-profile.prof
$ ProfileViewer my-profile.prof

DevTools/ProfileViewer/main.cpp

@@ -0,0 +1,33 @@
+#include "Profile.h"
+#include <LibGUI/GApplication.h>
+#include <LibGUI/GTreeView.h>
+#include <LibGUI/GWindow.h>
+#include <stdio.h>
+
+int main(int argc, char** argv)
+{
+    if (argc != 2) {
+        printf("usage: %s <profile-file>\n", argv[0]);
+        return 0;
+    }
+
+    auto profile = Profile::load_from_file(argv[1]);
+    if (!profile) {
+        fprintf(stderr, "Unable to load profile '%s'\n", argv[1]);
+        return 1;
+    }
+
+    GApplication app(argc, argv);
+
+    auto window = GWindow::construct();
+    window->set_title("ProfileViewer");
+    window->set_rect(100, 100, 800, 600);
+
+    auto tree_view = GTreeView::construct(nullptr);
+    tree_view->set_model(profile->model());
+
+    window->set_main_widget(tree_view);
+
+    window->show();
+    return app.exec();
+}