Revert "[heap] Use AdjustAmountOfExternalMemory to account freed array buffers."

This reverts commit 5ea58bde.

Reason for revert: potential perf regression.

BUG=chromium:748100

Original change's description:
> [heap] Use AdjustAmountOfExternalMemory to account freed array buffers.
> 
> Currently GC decrements the external memory counter directly bypassing
> the AdjustAmountOfExternalMemory. This is inconsistent with array
> buffer allocation, which actually uses the API to increment the counter.
> 
> Change-Id: I401087872213fdd60f1a40c99c8f459c14dc0608
> Reviewed-on: https://chromium-review.googlesource.com/582008
> Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
> Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#46835}

TBR=ulan@chromium.org,mlippautz@chromium.org

Change-Id: Ibde2acb9ae2e4274946124fc4606321b95c80758
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/583453Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46847}

src/heap/array-buffer-tracker-inl.h

@@ -44,8 +44,7 @@ void ArrayBufferTracker::Unregister(Heap* heap, JSArrayBuffer* buffer) {
     DCHECK_NOT_NULL(tracker);
     tracker->Remove(buffer, length);
   }
-  reinterpret_cast<v8::Isolate*>(heap->isolate())
-      ->AdjustAmountOfExternalAllocatedMemory(-static_cast<int64_t>(length));
+  heap->update_external_memory(-static_cast<intptr_t>(length));
 }
 
 void LocalArrayBufferTracker::Add(JSArrayBuffer* buffer, size_t length) {

src/heap/heap.cc

@@ -2256,14 +2256,6 @@ void Heap::UnregisterArrayBuffer(JSArrayBuffer* buffer) {
   ArrayBufferTracker::Unregister(this, buffer);
 }
 
-void Heap::account_external_memory_concurrently_freed() {
-  DCHECK_NE(gc_state_, NOT_IN_GC);
-  uint64_t delta = external_memory_concurrently_freed_.Value();
-  external_memory_concurrently_freed_.SetValue(0);
-  reinterpret_cast<v8::Isolate*>(isolate())
-      ->AdjustAmountOfExternalAllocatedMemory(delta);
-}
-
 void Heap::ConfigureInitialOldGenerationSize() {
   if (!old_generation_size_configured_ && tracer()->SurvivalEventsRecorded()) {
     old_generation_allocation_limit_ =

src/heap/heap.h

@@ -855,7 +855,10 @@ class Heap {
     external_memory_concurrently_freed_.Increment(freed);
   }
 
-  void account_external_memory_concurrently_freed();
+  void account_external_memory_concurrently_freed() {
+    external_memory_ -= external_memory_concurrently_freed_.Value();
+    external_memory_concurrently_freed_.SetValue(0);
+  }
 
   void DeoptMarkedAllocationSites();