[heap] Add histogram counters to track GC reasons.

src/heap/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_HEAP_H_
 #define V8_HEAP_HEAP_H_
 
 #include <cmath>
 #include <map>
 
@@ skipping 331 matching lines @@
 enum ArrayStorageAllocationMode {
   DONT_INITIALIZE_ARRAY_ELEMENTS,
   INITIALIZE_ARRAY_ELEMENTS_WITH_HOLE
 };
 
 enum class ClearRecordedSlots { kYes, kNo };
 
 enum class ClearBlackArea { kYes, kNo };
 
 enum class GarbageCollectionReason {
-  kUnknown,
-  kAllocationFailure,
-  kAllocationLimit,
-  kContextDisposal,
-  kCountersExtension,
-  kDebugger,
-  kDeserializer,
-  kExternalMemoryPressure,
-  kFinalizeMarkingViaStackGuard,
-  kFinalizeMarkingViaTask,
-  kFullHashtable,
-  kHeapProfiler,
-  kIdleTask,
-  kLastResort,
-  kLowMemoryNotification,
-  kMakeHeapIterable,
-  kMemoryPressure,
-  kMemoryReducer,
-  kRuntime,
-  kSamplingProfiler,
-  kSnapshotCreator,
-  kTesting
+  kUnknown = 0,
+  kAllocationFailure = 1,
+  kAllocationLimit = 2,
+  kContextDisposal = 3,
+  kCountersExtension = 4,
+  kDebugger = 5,
+  kDeserializer = 6,
+  kExternalMemoryPressure = 7,
+  kFinalizeMarkingViaStackGuard = 8,
+  kFinalizeMarkingViaTask = 9,
+  kFullHashtable = 10,
+  kHeapProfiler = 11,
+  kIdleTask = 12,
+  kLastResort = 13,
+  kLowMemoryNotification = 14,
+  kMakeHeapIterable = 15,
+  kMemoryPressure = 16,
+  kMemoryReducer = 17,
+  kRuntime = 18,
+  kSamplingProfiler = 19,
+  kSnapshotCreator = 20,
+  kTesting = 21
+  // If you add new items here, then update the incremental_marking_reason,
+  // mark_compact_reason, and scavenge_reason counters in counters.h.
+  // Also update src/tools/metrics/histograms/histograms.xml in chromium.
 };
 
 // A queue of objects promoted during scavenge. Each object is accompanied by
 // its size to avoid dereferencing a map pointer for scanning. The last page in
 // to-space is used for the promotion queue. On conflict during scavenge, the
 // promotion queue is allocated externally and all entries are copied to the
 // external queue.
 class PromotionQueue {
  public:
   explicit PromotionQueue(Heap* heap)
@@ skipping 2251 matching lines @@
   friend class LargeObjectSpace;
   friend class NewSpace;
   friend class PagedSpace;
   DISALLOW_COPY_AND_ASSIGN(AllocationObserver);
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_HEAP_HEAP_H_