[heap] Invoke OldGenerationAllocationCounter in Safepoint

OldGenerationAllocationCounter() needs to be invoked in safepoint,
otherwise invocation races with background threads incrementing the
counter.

Bug: v8:10315
Change-Id: Iab005582bab7ebf63e7a5a796b25690f499a99eb
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2235544
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68250}

src/heap/gc-tracer.cc

@@ -228,10 +228,6 @@ void GCTracer::Start(GarbageCollector collector,
   if (start_counter_ != 1) return;
 
   previous_ = current_;
-  double start_time = heap_->MonotonicallyIncreasingTimeInMs();
-  SampleAllocation(start_time, heap_->NewSpaceAllocationCounter(),
-                   heap_->OldGenerationAllocationCounter(),
-                   heap_->EmbedderAllocationCounter());
 
   switch (collector) {
     case SCAVENGER:
@@ -252,7 +248,7 @@ void GCTracer::Start(GarbageCollector collector,
   }
 
   current_.reduce_memory = heap_->ShouldReduceMemory();
-  current_.start_time = start_time;
+  current_.start_time = heap_->MonotonicallyIncreasingTimeInMs();
   current_.start_object_size = 0;
   current_.start_memory_size = 0;
   current_.start_holes_size = 0;
@@ -281,6 +277,10 @@ void GCTracer::Start(GarbageCollector collector,
 }
 
 void GCTracer::StartInSafepoint() {
+  SampleAllocation(current_.start_time, heap_->NewSpaceAllocationCounter(),
+                   heap_->OldGenerationAllocationCounter(),
+                   heap_->EmbedderAllocationCounter());
+
   current_.start_object_size = heap_->SizeOfObjects();
   current_.start_memory_size = heap_->memory_allocator()->Size();
   current_.start_holes_size = CountTotalHolesSize(heap_);