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/Profile.h

@@ -0,0 +1,88 @@
+#pragma once
+
+#include <AK/JsonArray.h>
+#include <AK/JsonObject.h>
+#include <AK/JsonValue.h>
+#include <AK/NonnullRefPtrVector.h>
+#include <AK/OwnPtr.h>
+
+class GModel;
+class ProfileModel;
+
+class ProfileNode : public RefCounted<ProfileNode> {
+public:
+    static NonnullRefPtr<ProfileNode> create(const String& symbol, u32 address, u32 offset)
+    {
+        return adopt(*new ProfileNode(symbol, address, offset));
+    }
+
+    const String& symbol() const { return m_symbol; }
+    u32 address() const { return m_address; }
+    u32 offset() const { return m_offset; }
+
+    u32 sample_count() const { return m_sample_count; }
+
+    int child_count() const { return m_children.size(); }
+    const Vector<NonnullRefPtr<ProfileNode>>& children() const { return m_children; }
+
+    void add_child(ProfileNode& child)
+    {
+        if (child.m_parent == this)
+            return;
+        ASSERT(!child.m_parent);
+        child.m_parent = this;
+        m_children.append(child);
+    }
+
+    ProfileNode& find_or_create_child(const String& symbol, u32 address, u32 offset)
+    {
+        for (int i = 0; i < m_children.size(); ++i) {
+            auto& child = m_children[i];
+            if (child->symbol() == symbol) {
+                return child;
+            }
+        }
+        auto new_child = ProfileNode::create(symbol, address, offset);
+        m_children.append(new_child);
+        return new_child;
+    };
+
+    ProfileNode* parent() { return m_parent; }
+    const ProfileNode* parent() const { return m_parent; }
+
+    void increment_sample_count() { ++m_sample_count; }
+
+    void sort_children();
+
+private:
+    explicit ProfileNode(const String& symbol, u32 address, u32 offset)
+        : m_symbol(symbol)
+        , m_address(address)
+        , m_offset(offset)
+    {
+    }
+
+    ProfileNode* m_parent { nullptr };
+    String m_symbol;
+    u32 m_address { 0 };
+    u32 m_offset { 0 };
+    u32 m_sample_count { 0 };
+    Vector<NonnullRefPtr<ProfileNode>> m_children;
+};
+
+class Profile {
+public:
+    static OwnPtr<Profile> load_from_file(const StringView& path);
+    ~Profile();
+
+    GModel& model();
+
+    const NonnullRefPtrVector<ProfileNode>& roots() const { return m_roots; }
+
+private:
+    explicit Profile(const JsonArray&, NonnullRefPtrVector<ProfileNode>&&);
+
+    JsonArray m_json;
+    RefPtr<ProfileModel> m_model;
+    NonnullRefPtrVector<ProfileNode> m_roots;
+};