[heap] Do not schedule follow-up GCs on memory pressure signal

Upon receiving a memory pressure signal V8 performs one GC and also
schedules three follow-up GCs. This may be problematic for performance
if the memory pressure signals are generated periodically.

This patch makes V8's memory pressure handler more lightweight by doing
only one GC.

Bug: chromium:1072746
Change-Id: I242534bd2c27a68188bb5e3a6b4092118c1b486c
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2169930Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Hannes Payer <hpayer@chromium.org>
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67422}

src/heap/heap.cc

@@ -3773,12 +3773,6 @@ void Heap::CheckMemoryPressure() {
                               GarbageCollectionReason::kMemoryPressure);
     }
   }
-  if (memory_reducer_) {
-    MemoryReducer::Event event;
-    event.type = MemoryReducer::kPossibleGarbage;
-    event.time_ms = MonotonicallyIncreasingTimeInMs();
-    memory_reducer_->NotifyPossibleGarbage(event);
-  }
 }
 
 void Heap::CollectGarbageOnMemoryPressure() {