Reland "[heap] Updated spaces Verify to check external memory count."

This is a reland of 6b810dad

Original change's description:
> [heap] Updated spaces Verify to check external memory count.
> 
> Bug: chromium:845409
> Change-Id: Ieb690f2d6ed699f306f1ff351cb5f62d9e2db860
> Reviewed-on: https://chromium-review.googlesource.com/1114820
> Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
> Commit-Queue: Rodrigo Bruno <rfbpb@google.com>
> Cr-Commit-Position: refs/heads/master@{#54035}

Bug: chromium:845409
Change-Id: I71576bd397ca70d9ce76de279c2d9d1fa5a70596
Reviewed-on: https://chromium-review.googlesource.com/1120365Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Rodrigo Bruno <rfbpb@google.com>
Cr-Commit-Position: refs/heads/master@{#54115}

src/heap/spaces.cc

@@ -1899,6 +1899,12 @@ void PagedSpace::Print() {}
 void PagedSpace::Verify(Isolate* isolate, ObjectVisitor* visitor) {
   bool allocation_pointer_found_in_space =
       (allocation_info_.top() == allocation_info_.limit());
+  size_t external_backing_store_bytes[kNumTypes];
+
+  for (int i = 0; i < kNumTypes; i++) {
+    external_backing_store_bytes[static_cast<ExternalBackingStoreType>(i)] = 0;
+  }
+
   for (Page* page : *this) {
     CHECK(page->owner() == this);
     if (page == Page::FromAllocationAreaAddress(allocation_info_.top())) {
@@ -1908,6 +1914,12 @@ void PagedSpace::Verify(Isolate* isolate, ObjectVisitor* visitor) {
     HeapObjectIterator it(page);
     Address end_of_previous_object = page->area_start();
     Address top = page->area_end();
+
+    for (int i = 0; i < kNumTypes; i++) {
+      ExternalBackingStoreType t = static_cast<ExternalBackingStoreType>(i);
+      external_backing_store_bytes[t] += page->ExternalBackingStoreBytes(t);
+    }
+
     for (HeapObject* object = it.Next(); object != nullptr;
          object = it.Next()) {
       CHECK(end_of_previous_object <= object->address());
@@ -1936,6 +1948,10 @@ void PagedSpace::Verify(Isolate* isolate, ObjectVisitor* visitor) {
       end_of_previous_object = object->address() + size;
     }
   }
+  for (int i = 0; i < kNumTypes; i++) {
+    ExternalBackingStoreType t = static_cast<ExternalBackingStoreType>(i);
+    CHECK_EQ(external_backing_store_bytes[t], ExternalBackingStoreBytes(t));
+  }
   CHECK(allocation_pointer_found_in_space);
 #ifdef DEBUG
   VerifyCountersAfterSweeping();
@@ -2634,6 +2650,12 @@ void SemiSpace::Print() {}
 #ifdef VERIFY_HEAP
 void SemiSpace::Verify() {
   bool is_from_space = (id_ == kFromSpace);
+  size_t external_backing_store_bytes[kNumTypes];
+
+  for (int i = 0; i < kNumTypes; i++) {
+    external_backing_store_bytes[static_cast<ExternalBackingStoreType>(i)] = 0;
+  }
+
   for (Page* page : *this) {
     CHECK_EQ(page->owner(), this);
     CHECK(page->InNewSpace());
@@ -2652,9 +2674,18 @@ void SemiSpace::Verify() {
             !page->IsFlagSet(MemoryChunk::POINTERS_FROM_HERE_ARE_INTERESTING));
       }
     }
+    for (int i = 0; i < kNumTypes; i++) {
+      ExternalBackingStoreType t = static_cast<ExternalBackingStoreType>(i);
+      external_backing_store_bytes[t] += page->ExternalBackingStoreBytes(t);
+    }
+
     CHECK_IMPLIES(page->list_node().prev(),
                   page->list_node().prev()->list_node().next() == page);
   }
+  for (int i = 0; i < kNumTypes; i++) {
+    ExternalBackingStoreType t = static_cast<ExternalBackingStoreType>(i);
+    CHECK_EQ(external_backing_store_bytes[t], ExternalBackingStoreBytes(t));
+  }
 }
 #endif
 
@@ -3480,6 +3511,12 @@ std::unique_ptr<ObjectIterator> LargeObjectSpace::GetObjectIterator() {
 // We do not assume that the large object iterator works, because it depends
 // on the invariants we are checking during verification.
 void LargeObjectSpace::Verify(Isolate* isolate) {
+  size_t external_backing_store_bytes[kNumTypes];
+
+  for (int i = 0; i < kNumTypes; i++) {
+    external_backing_store_bytes[static_cast<ExternalBackingStoreType>(i)] = 0;
+  }
+
   for (LargePage* chunk = first_page(); chunk != nullptr;
        chunk = chunk->next_page()) {
     // Each chunk contains an object that starts at the large object page's
@@ -3536,6 +3573,14 @@ void LargeObjectSpace::Verify(Isolate* isolate) {
         }
       }
     }
+    for (int i = 0; i < kNumTypes; i++) {
+      ExternalBackingStoreType t = static_cast<ExternalBackingStoreType>(i);
+      external_backing_store_bytes[t] += chunk->ExternalBackingStoreBytes(t);
+    }
+  }
+  for (int i = 0; i < kNumTypes; i++) {
+    ExternalBackingStoreType t = static_cast<ExternalBackingStoreType>(i);
+    CHECK_EQ(external_backing_store_bytes[t], ExternalBackingStoreBytes(t));
   }
 }
 #endif