ProfileViewer: Precompute the timestamp and "in kernel?" per sample

Instead of fetching these from JSON in every paint event, we now have a
separate "SampleData" vector that can be iterated.

This optimization was made possible by profiling ProfileViewer and then
analyzing the profile with ProfileViewer! :^)

DevTools/ProfileViewer/Profile.cpp

@@ -12,6 +12,13 @@ Profile::Profile(const JsonArray& json)
 
     m_model = ProfileModel::create(*this);
     rebuild_tree();
+
+    m_sample_data.ensure_capacity(m_json.size());
+    m_json.for_each([&](const JsonValue& sample) {
+        u64 timestamp = sample.as_object().get("timestamp").to_number<u64>() - m_first_timestamp;
+        bool in_kernel = sample.as_object().get("frames").as_array().at(1).as_object().get("address").to_number<u32>() < (8 * MB);
+        m_sample_data.append({ timestamp, in_kernel });
+    });
 }
 
 Profile::~Profile()

DevTools/ProfileViewer/Profile.h

@@ -90,6 +90,13 @@ public:
         });
     }
 
+    struct SampleData {
+        u64 timestamp { 0 };
+        bool in_kernel { false };
+    };
+
+    const Vector<SampleData>& sample_data() const { return m_sample_data; }
+
     u64 length_in_ms() const { return m_last_timestamp - m_first_timestamp; }
     u64 first_timestamp() const { return m_first_timestamp; }
     u64 last_timestamp() const { return m_first_timestamp; }
@@ -109,6 +116,8 @@ private:
     u64 m_first_timestamp { 0 };
     u64 m_last_timestamp { 0 };
 
+    Vector<SampleData> m_sample_data;
+
     bool m_has_timestamp_filter_range { false };
     u64 m_timestamp_filter_range_start { 0 };
     u64 m_timestamp_filter_range_end { 0 };

DevTools/ProfileViewer/ProfileTimelineWidget.cpp

@@ -28,16 +28,16 @@ void ProfileTimelineWidget::paint_event(GPaintEvent& event)
 
     float column_width = (float)frame_inner_rect().width() / (float)m_profile.length_in_ms();
 
-    m_profile.for_each_sample([&](const JsonObject& sample) {
-        u64 t = sample.get("timestamp").to_number<u64>() - m_profile.first_timestamp();
+    for (auto& sample : m_profile.sample_data()) {
+        u64 t = sample.timestamp;
         int x = (int)((float)t * column_width);
         int cw = max(1, (int)column_width);
 
-        bool in_kernel = sample.get("frames").as_array().at(1).as_object().get("address").to_number<u32>() < (8 * MB);
+        bool in_kernel = sample.in_kernel;
         Color color = in_kernel ? Color::from_rgb(0xc25e5a) : Color::from_rgb(0x5a65c2);
         for (int i = 0; i < cw; ++i)
             painter.draw_line({ x + i, frame_thickness() }, { x + i, height() - frame_thickness() * 2 }, color);
-    });
+    }
 
     u64 normalized_start_time = min(m_select_start_time, m_select_end_time);
     u64 normalized_end_time = max(m_select_start_time, m_select_end_time);