[heap] Memory reducer calls GC with kGCCallbackFlagCollectAllExternalMemory flag.

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 <vector>
 
@@ skipping 1221 matching lines @@
   void ClearRecordedSlotRange(Address start, Address end);
 
   bool HasRecordedSlot(HeapObject* object, Object** slot);
 
   // ===========================================================================
   // Incremental marking API. ==================================================
   // ===========================================================================
 
   // Start incremental marking and ensure that idle time handler can perform
   // incremental steps.
-  void StartIdleIncrementalMarking(GarbageCollectionReason gc_reason);
+  void StartIdleIncrementalMarking(
+      GarbageCollectionReason gc_reason,
+      GCCallbackFlags gc_callback_flags = GCCallbackFlags::kNoGCCallbackFlags);
 
   // Starts incremental marking assuming incremental marking is currently
   // stopped.
   void StartIncrementalMarking(
       int gc_flags, GarbageCollectionReason gc_reason,
       GCCallbackFlags gc_callback_flags = GCCallbackFlags::kNoGCCallbackFlags);
 
   void StartIncrementalMarkingIfAllocationLimitIsReached(
       int gc_flags,
       GCCallbackFlags gc_callback_flags = GCCallbackFlags::kNoGCCallbackFlags);
@@ skipping 1399 matching lines @@
   friend class PagedSpace;
   DISALLOW_COPY_AND_ASSIGN(AllocationObserver);
 };
 
 V8_EXPORT_PRIVATE const char* AllocationSpaceName(AllocationSpace space);
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_HEAP_HEAP_H_