Kernel+Profiler: Track lost time between profiler timer ticks

We can lose profiling timer events for a few reasons, for example
disabled interrupts or system slowness. This accounts for lost
time between CPU samples by adding a field lost_samples to each
profiling event which tracks how many samples were lost immediately
preceding the event.

Userland/DevTools/Profiler/TimelineTrack.cpp

@@ -78,7 +78,7 @@ void TimelineTrack::paint_event(GUI::PaintEvent& event)
         }
 
         auto& histogram = event.in_kernel ? kernel_histogram : usermode_histogram;
-        histogram.insert(clamp_timestamp(event.timestamp), 1);
+        histogram.insert(clamp_timestamp(event.timestamp), 1 + event.lost_samples);
     }
 
     decltype(kernel_histogram.at(0)) max_value = 0;