[debugger] track debugger feature usage via histogram.

src/profiler/cpu-profiler.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/profiler/cpu-profiler.h"
 
+#include "src/debug/debug.h"
 #include "src/deoptimizer.h"
 #include "src/frames-inl.h"
 #include "src/locked-queue-inl.h"
 #include "src/log-inl.h"
 #include "src/profiler/cpu-profiler-inl.h"
 #include "src/vm-state-inl.h"
 
 #include "include/v8-profiler.h"
 
 namespace v8 {
@@ skipping 414 matching lines @@
 
 void CpuProfiler::StartProfiling(const char* title, bool record_samples) {
   if (profiles_->StartProfiling(title, record_samples)) {
     StartProcessorIfNotStarted();
   }
 }
 
 
 void CpuProfiler::StartProfiling(String* title, bool record_samples) {
   StartProfiling(profiles_->GetName(title), record_samples);
+  isolate_->debug()->feature_tracker()->Track(DebugFeatureTracker::kProfiler);
 }
 
 
 void CpuProfiler::StartProcessorIfNotStarted() {
   if (processor_ != NULL) {
     processor_->AddCurrentStack(isolate_);
     return;
   }
   Logger* logger = isolate_->logger();
   // Disable logging when using the new implementation.
@@ skipping 68 matching lines @@
     Builtins::Name id = static_cast<Builtins::Name>(i);
     rec->start = builtins->builtin(id)->address();
     rec->builtin_id = id;
     processor_->Enqueue(evt_rec);
   }
 }
 
 
 }  // namespace internal
 }  // namespace v8