deps: V8: cherry-pick 502c6ae6 from upstream

Original commit message:
  [heap] Activate memory reducer on external memory activity.

  BUG=chromium:728228,chromium:626082
  CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_chromium_rel_ng

  Review-Url: https://codereview.chromium.org/2917853004
  Cr-Commit-Position: refs/heads/master@{#45671}

PR-URL: #21269
Fixes: #21021
Reviewed-By: Myles Borins <myles.borins@gmail.com>

deps/v8/include/v8-version.h

@@ -11,7 +11,7 @@
 #define V8_MAJOR_VERSION 6
 #define V8_MINOR_VERSION 2
 #define V8_BUILD_NUMBER 414
-#define V8_PATCH_LEVEL 55
+#define V8_PATCH_LEVEL 56
 
 // Use 1 for candidates and 0 otherwise.
 // (Boolean macro values are not supported by all preprocessors.)

deps/v8/include/v8.h

@@ -7770,6 +7770,7 @@ class V8_EXPORT Isolate {
   friend class PersistentValueMapBase;
 
   void ReportExternalAllocationLimitReached();
+  void CheckMemoryPressure();
 };
 
 class V8_EXPORT StartupData {
@@ -9019,6 +9020,8 @@ class Internals {
   static const int kExternalMemoryOffset = 4 * kApiPointerSize;
   static const int kExternalMemoryLimitOffset =
       kExternalMemoryOffset + kApiInt64Size;
+  static const int kExternalMemoryAtLastMarkCompactOffset =
+      kExternalMemoryLimitOffset + kApiInt64Size;
   static const int kIsolateRootsOffset = kExternalMemoryLimitOffset +
                                          kApiInt64Size + kApiInt64Size +
                                          kApiPointerSize + kApiPointerSize;
@@ -10244,13 +10247,28 @@ uint32_t Isolate::GetNumberOfDataSlots() {
 
 int64_t Isolate::AdjustAmountOfExternalAllocatedMemory(
     int64_t change_in_bytes) {
+  const int64_t kMemoryReducerActivationLimit = 1024 * 1024;
   typedef internal::Internals I;
   int64_t* external_memory = reinterpret_cast<int64_t*>(
       reinterpret_cast<uint8_t*>(this) + I::kExternalMemoryOffset);
   const int64_t external_memory_limit = *reinterpret_cast<int64_t*>(
       reinterpret_cast<uint8_t*>(this) + I::kExternalMemoryLimitOffset);
+  int64_t* external_memory_at_last_mc =
+      reinterpret_cast<int64_t*>(reinterpret_cast<uint8_t*>(this) +
+                                 I::kExternalMemoryAtLastMarkCompactOffset);
   const int64_t amount = *external_memory + change_in_bytes;
+
   *external_memory = amount;
+
+  int64_t allocation_diff_since_last_mc =
+      *external_memory_at_last_mc - *external_memory;
+  allocation_diff_since_last_mc = allocation_diff_since_last_mc < 0
+                                      ? -allocation_diff_since_last_mc
+                                      : allocation_diff_since_last_mc;
+  if (allocation_diff_since_last_mc > kMemoryReducerActivationLimit) {
+    CheckMemoryPressure();
+  }
+
   if (change_in_bytes > 0 && amount > external_memory_limit) {
     ReportExternalAllocationLimitReached();
   }

deps/v8/src/api.cc

@@ -8405,6 +8405,10 @@ void Isolate::ReportExternalAllocationLimitReached() {
   heap->ReportExternalMemoryPressure();
 }
 
+void Isolate::CheckMemoryPressure() {
+  i::Heap* heap = reinterpret_cast<i::Isolate*>(this)->heap();
+  heap->CheckMemoryPressure();
+}
 
 HeapProfiler* Isolate::GetHeapProfiler() {
   i::HeapProfiler* heap_profiler =

deps/v8/src/heap/heap.cc

@@ -4816,10 +4816,12 @@ void Heap::CheckMemoryPressure() {
                               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() {

deps/v8/src/isolate.cc

@@ -2837,6 +2837,9 @@ bool Isolate::Init(StartupDeserializer* des) {
            Internals::kExternalMemoryOffset);
   CHECK_EQ(static_cast<int>(OFFSET_OF(Isolate, heap_.external_memory_limit_)),
            Internals::kExternalMemoryLimitOffset);
+  CHECK_EQ(static_cast<int>(
+               OFFSET_OF(Isolate, heap_.external_memory_at_last_mark_compact_)),
+           Internals::kExternalMemoryAtLastMarkCompactOffset);
 
   time_millis_at_init_ = heap_.MonotonicallyIncreasingTimeInMs();