[test-heap] fixed test to avoid internal call that will be removed

Bug: chromium:845409
Change-Id: I73a5db1c09e0adb3eab0ee0bdf675edbdea6c6e7
Reviewed-on: https://chromium-review.googlesource.com/1170762Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Rodrigo Bruno <rfbpb@google.com>
Cr-Commit-Position: refs/heads/master@{#55045}

test/cctest/heap/test-heap.cc

@@ -5660,7 +5660,7 @@ TEST(Regress618958) {
   v8::HandleScope scope(CcTest::isolate());
   Heap* heap = CcTest::heap();
   bool isolate_is_locked = true;
-  heap->update_external_memory(100 * MB);
+  CcTest::isolate()->AdjustAmountOfExternalAllocatedMemory(100 * MB);
   int mark_sweep_count_before = heap->ms_count();
   heap->MemoryPressureNotification(MemoryPressureLevel::kCritical,
                                    isolate_is_locked);