[debugger] track debugger feature usage via histogram.

src/debug/debug.h

 // 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.
 
 #ifndef V8_DEBUG_DEBUG_H_
 #define V8_DEBUG_DEBUG_H_
 
 #include "src/allocation.h"
 #include "src/arguments.h"
 #include "src/assembler.h"
@@ skipping 325 matching lines @@
   void Put(const CommandMessage& message);
   void Clear();
  private:
   Logger* logger_;
   CommandMessageQueue queue_;
   mutable base::Mutex mutex_;
   DISALLOW_COPY_AND_ASSIGN(LockingCommandMessageQueue);
 };
 
 
+class DebugFeatureTracker {
+ public:
+  enum Feature {
+    kActive = 1,
+    kBreakPoint = 2,
+    kStepping = 3,
+    kHeapSnapshot = 4,
+    kAllocationTracking = 5,
+    kProfiler = 6,
+    kLiveEdit = 7,
+  };
+
+  explicit DebugFeatureTracker(Isolate* isolate)
+      : isolate_(isolate), bitfield_(0) {}
+  void Track(Feature feature);
+
+ private:
+  Isolate* isolate_;
+  uint32_t bitfield_;
+};
+
+
 // This class contains the debugger support. The main purpose is to handle
 // setting break points in the code.
 //
 // This class controls the debug info for all functions which currently have
 // active breakpoints in them. This debug info is held in the heap root object
 // debug_info which is a FixedArray. Each entry in this list is of class
 // DebugInfo.
 class Debug {
  public:
   // Debug event triggers.
@@ skipping 145 matching lines @@
     Object*** address = &thread_local_.restarter_frame_function_pointer_;
     return reinterpret_cast<Address>(address);
   }
 
   Address step_in_fp_addr() {
     return reinterpret_cast<Address>(&thread_local_.step_into_fp_);
   }
 
   StepAction last_step_action() { return thread_local_.last_step_action_; }
 
+  DebugFeatureTracker* feature_tracker() { return &feature_tracker_; }
+
  private:
   explicit Debug(Isolate* isolate);
 
   void UpdateState();
   void Unload();
   void SetNextBreakId() {
     thread_local_.break_id_ = ++thread_local_.break_count_;
   }
 
   // Check whether there are commands in the command queue.
@@ skipping 78 matching lines @@
   bool break_on_exception_;
   bool break_on_uncaught_exception_;
 
   DebugInfoListNode* debug_info_list_;  // List of active debug info objects.
 
   // Storage location for jump when exiting debug break calls.
   // Note that this address is not GC safe.  It should be computed immediately
   // before returning to the DebugBreakCallHelper.
   Address after_break_target_;
 
+  // Used to collect histogram data on debugger feature usage.
+  DebugFeatureTracker feature_tracker_;
+
   // Per-thread data.
   class ThreadLocal {
    public:
     // Top debugger entry.
     base::AtomicWord current_debug_scope_;
 
     // Counter for generating next break id.
     int break_count_;
 
     // Current break id.
@@ skipping 142 matching lines @@
 
   static void PatchDebugBreakSlot(Address pc, Handle<Code> code);
   static void ClearDebugBreakSlot(Address pc);
 };
 
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_DEBUG_DEBUG_H_