[heap] Memory reducer calls GC with kGCCallbackFlagCollectAllExternalMemory flag.

BUG=chromium:718484

Review-Url: https://codereview.chromium.org/2863943002
Cr-Commit-Position: refs/heads/master@{#45128}

src/heap/heap.cc

@@ -1115,10 +1115,12 @@ void Heap::StartIncrementalMarkingIfAllocationLimitIsReached(
   }
 }
 
-void Heap::StartIdleIncrementalMarking(GarbageCollectionReason gc_reason) {
+void Heap::StartIdleIncrementalMarking(
+    GarbageCollectionReason gc_reason,
+    const GCCallbackFlags gc_callback_flags) {
   gc_idle_time_handler_->ResetNoProgressCounter();
   StartIncrementalMarking(kReduceMemoryFootprintMask, gc_reason,
-                          kNoGCCallbackFlags);
+                          gc_callback_flags);
 }
 
 
@@ -4232,7 +4234,7 @@ void Heap::FinalizeIncrementalMarkingIfComplete(
              (mark_compact_collector()->marking_deque()->IsEmpty() &&
               local_embedder_heap_tracer()
                   ->ShouldFinalizeIncrementalMarking())) {
-    CollectAllGarbage(current_gc_flags_, gc_reason);
+    CollectAllGarbage(current_gc_flags_, gc_reason, current_gc_callback_flags_);
   }
 }
 

src/heap/heap.h

@@ -1239,7 +1239,9 @@ class Heap {
 
   // 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.

src/heap/memory-reducer.cc

@@ -66,7 +66,8 @@ void MemoryReducer::NotifyTimer(const Event& event) {
                                             state_.started_gcs);
     }
     heap()->StartIdleIncrementalMarking(
-        GarbageCollectionReason::kMemoryReducer);
+        GarbageCollectionReason::kMemoryReducer,
+        kGCCallbackFlagCollectAllExternalMemory);
   } else if (state_.action == kWait) {
     if (!heap()->incremental_marking()->IsStopped() &&
         heap()->ShouldOptimizeForMemoryUsage()) {