[heap] Activate memory reducer on external memory activity.

src/heap/heap.cc

 // 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.
 
 #include "src/heap/heap.h"
 
 #include <unordered_map>
 #include <unordered_set>
 
 #include "src/accessors.h"
@@ skipping 4498 matching lines @@
     }
   }
   if (memory_pressure_level_.Value() == MemoryPressureLevel::kCritical) {
     CollectGarbageOnMemoryPressure();
   } else if (memory_pressure_level_.Value() == MemoryPressureLevel::kModerate) {
     if (FLAG_incremental_marking && incremental_marking()->IsStopped()) {
       StartIncrementalMarking(kReduceMemoryFootprintMask,
                               GarbageCollectionReason::kMemoryPressure);
     }
   }
-  MemoryReducer::Event event;
-  event.type = MemoryReducer::kPossibleGarbage;
-  event.time_ms = MonotonicallyIncreasingTimeInMs();
-  memory_reducer_->NotifyPossibleGarbage(event);
+  if (memory_reducer_) {
+    MemoryReducer::Event event;
+    event.type = MemoryReducer::kPossibleGarbage;
+    event.time_ms = MonotonicallyIncreasingTimeInMs();
+    memory_reducer_->NotifyPossibleGarbage(event);
+  }
 }
 
 void Heap::CollectGarbageOnMemoryPressure() {
   const int kGarbageThresholdInBytes = 8 * MB;
   const double kGarbageThresholdAsFractionOfTotalMemory = 0.1;
   // This constant is the maximum response time in RAIL performance model.
   const double kMaxMemoryPressurePauseMs = 100;
 
   double start = MonotonicallyIncreasingTimeInMs();
   CollectAllGarbage(kReduceMemoryFootprintMask | kAbortIncrementalMarkingMask,
@@ skipping 2074 matching lines @@
     case LO_SPACE:
       return "LO_SPACE";
     default:
       UNREACHABLE();
   }
   return NULL;
 }
 
 }  // namespace internal
 }  // namespace v8