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/Profile.h

@@ -166,6 +166,7 @@ public:
         String executable;
         int pid { 0 };
         int tid { 0 };
+        u32 lost_samples { 0 };
         bool in_kernel { false };
         Vector<Frame> frames;
     };