[heap] Preparing memory chunks to contain external memory counters.

Bug: chromium:845409
Change-Id: Id4f1b93f0992e15ed592156c7dec7d15828e4c42
Reviewed-on: https://chromium-review.googlesource.com/1113552Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Rodrigo Bruno <rfbpb@google.com>
Cr-Commit-Position: refs/heads/master@{#54014}

src/heap/spaces.cc

@@ -631,6 +631,12 @@ MemoryChunk* MemoryChunk::Initialize(Heap* heap, Address base, size_t size,
   chunk->young_generation_bitmap_ = nullptr;
   chunk->local_tracker_ = nullptr;
 
+  chunk->external_backing_store_bytes_[ExternalBackingStoreType::kOther] = 0;
+  chunk->external_backing_store_bytes_[ExternalBackingStoreType::kArrayBuffer] =
+      0;
+  chunk->external_backing_store_bytes_
+      [ExternalBackingStoreType::kExternalString] = 0;
+
   for (int i = kFirstCategory; i < kNumberOfCategories; i++) {
     chunk->categories_[i] = nullptr;
   }

src/heap/spaces.h

@@ -367,13 +367,15 @@ class MemoryChunk {
       + kIntptrSize       // std::atomic<intptr_t> live_byte_count_
       + kPointerSize * NUMBER_OF_REMEMBERED_SET_TYPES  // SlotSet* array
       + kPointerSize * NUMBER_OF_REMEMBERED_SET_TYPES  // TypedSlotSet* array
-      + kPointerSize      // InvalidatedSlots* invalidated_slots_
-      + kPointerSize      // SkipList* skip_list_
-      + kPointerSize      // AtomicValue high_water_mark_
-      + kPointerSize      // base::Mutex* mutex_
-      + kPointerSize      // base::AtomicWord concurrent_sweeping_
-      + kPointerSize      // base::Mutex* page_protection_change_mutex_
-      + kPointerSize      // unitptr_t write_unprotect_counter_
+      + kPointerSize  // InvalidatedSlots* invalidated_slots_
+      + kPointerSize  // SkipList* skip_list_
+      + kPointerSize  // AtomicValue high_water_mark_
+      + kPointerSize  // base::Mutex* mutex_
+      + kPointerSize  // base::AtomicWord concurrent_sweeping_
+      + kPointerSize  // base::Mutex* page_protection_change_mutex_
+      + kPointerSize  // unitptr_t write_unprotect_counter_
+      + kSizetSize * kNumTypes
+      // std::atomic<size_t> external_backing_store_bytes_
       + kSizetSize        // size_t allocated_bytes_
       + kSizetSize        // size_t wasted_memory_
       + kPointerSize * 2  // base::ListNode
@@ -536,6 +538,15 @@ class MemoryChunk {
     }
   }
 
+  void IncrementExternalBackingStoreBytes(size_t amount,
+                                          ExternalBackingStoreType type) {
+    external_backing_store_bytes_[type] += amount;
+  }
+  void DecrementExternalBackingStoreBytes(size_t amount,
+                                          ExternalBackingStoreType type) {
+    external_backing_store_bytes_[type] -= amount;
+  }
+
   inline uint32_t AddressToMarkbitIndex(Address addr) const {
     return static_cast<uint32_t>(addr - this->address()) >> kPointerSizeLog2;
   }
@@ -691,6 +702,10 @@ class MemoryChunk {
   // Byte allocated on the page, which includes all objects on the page
   // and the linear allocation area.
   size_t allocated_bytes_;
+
+  // Tracks off-heap memory used by this memory chunk.
+  std::atomic<size_t> external_backing_store_bytes_[kNumTypes];
+
   // Freed memory that was not added to the free list.
   size_t wasted_memory_;