Added histogram to track distribution of requested idle notifications.

src/heap.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_HEAP_H_
 #define V8_HEAP_H_
 
 #include <cmath>
 
 #include "src/allocation.h"
@@ skipping 2259 matching lines @@
 
   // These two counters are monotomically increasing and never reset.
   size_t full_codegen_bytes_generated_;
   size_t crankshaft_codegen_bytes_generated_;
 
   // If the --deopt_every_n_garbage_collections flag is set to a positive value,
   // this variable holds the number of garbage collections since the last
   // deoptimization triggered by garbage collection.
   int gcs_since_last_deopt_;
 
+  static const int kMaxIdleNotificationHistogramSample = 1000;
+
+  // A histogram that displays the distribution of idle notification calls.
+  void* idle_notification_histogram_;

[rmcilroy, 2014/07/25 09:38:29]

I'd probably call this idle_notification_hint_histogram_ (or maybe something
like idle_gc_allotted_time_histogram_ for the new scheduler based time).

Also, any reason this isn't in counters.h - there is already a
gc_idle_notification in HISTOGRAM_TIMER_LIST.

[Hannes Payer (out of office), 2014/07/25 10:08:20]

Yeah, we do not really have a category for this counter. I could create a "fake"
HistogramTimer. The only similar histogram I found was the script_histogram_.
WDYT?

+
 #ifdef VERIFY_HEAP
   int no_weak_object_verification_scope_depth_;
 #endif
 
   static const int kAllocationSiteScratchpadSize = 256;
   int allocation_sites_scratchpad_length_;
 
   static const int kMaxMarkSweepsInIdleRound = 7;
   static const int kIdleScavengeThreshold = 5;
 
@@ skipping 493 matching lines @@
   DisallowHeapAllocation no_allocation;  // i.e. no gc allowed.
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(PathTracer);
 };
 #endif  // DEBUG
 
 } }  // namespace v8::internal
 
 #endif  // V8_HEAP_H_