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/SamplesModel.h

@@ -25,6 +25,7 @@ public:
         ProcessID,
         ThreadID,
         ExecutableName,
+        LostSamples,
         InnermostStackFrame,
         __Count
     };