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/ProfileModel.cpp

@@ -0,0 +1,83 @@
+#include "ProfileModel.h"
+#include "Profile.h"
+#include <AK/StringBuilder.h>
+#include <ctype.h>
+#include <stdio.h>
+
+ProfileModel::ProfileModel(Profile& profile)
+    : m_profile(profile)
+{
+    m_frame_icon.set_bitmap_for_size(16, GraphicsBitmap::load_from_file("/res/icons/16x16/inspector-object.png"));
+}
+
+ProfileModel::~ProfileModel()
+{
+}
+
+GModelIndex ProfileModel::index(int row, int column, const GModelIndex& parent) const
+{
+    if (!parent.is_valid()) {
+        if (m_profile.roots().is_empty())
+            return {};
+        return create_index(row, column, &m_profile.roots().at(row));
+    }
+    auto& remote_parent = *static_cast<ProfileNode*>(parent.internal_data());
+    return create_index(row, column, remote_parent.children().at(row).ptr());
+}
+
+GModelIndex ProfileModel::parent_index(const GModelIndex& index) const
+{
+    if (!index.is_valid())
+        return {};
+    auto& node = *static_cast<ProfileNode*>(index.internal_data());
+    if (!node.parent())
+        return {};
+
+    // NOTE: If the parent has no parent, it's a root, so we have to look among the remote roots.
+    if (!node.parent()->parent()) {
+        for (int row = 0; row < m_profile.roots().size(); ++row) {
+            if (&m_profile.roots()[row] == node.parent())
+                return create_index(row, 0, node.parent());
+        }
+        ASSERT_NOT_REACHED();
+        return {};
+    }
+
+    for (int row = 0; row < node.parent()->parent()->children().size(); ++row) {
+        if (node.parent()->parent()->children()[row].ptr() == node.parent())
+            return create_index(row, 0, node.parent());
+    }
+
+    ASSERT_NOT_REACHED();
+    return {};
+}
+
+int ProfileModel::row_count(const GModelIndex& index) const
+{
+    if (!index.is_valid())
+        return m_profile.roots().size();
+    auto& node = *static_cast<ProfileNode*>(index.internal_data());
+    return node.children().size();
+}
+
+int ProfileModel::column_count(const GModelIndex&) const
+{
+    return 1;
+}
+
+GVariant ProfileModel::data(const GModelIndex& index, Role role) const
+{
+    auto* node = static_cast<ProfileNode*>(index.internal_data());
+    if (role == Role::Icon) {
+        return m_frame_icon;
+    }
+    if (role == Role::Display) {
+        return String::format("%s (%u)", node->symbol().characters(), node->sample_count());
+    }
+    return {};
+}
+
+void ProfileModel::update()
+{
+    did_update();
+}