cppgc: young-gen: Run minor GC only from task.

Oilpan minor GC currently doesn't support running with the stack. The CL
changes minor GCs to run only when running from task.

Bug: chromium:1029379
Change-Id: I96552772e9c3b653a137f48bbaae44278db8f014
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3571891Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Anton Bikineev <bikineev@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79800}

src/heap/heap.cc

@@ -2348,7 +2348,11 @@ size_t Heap::PerformGarbageCollection(
     local_embedder_heap_tracer()->TraceEpilogue();
   }
 
-  if (collector == GarbageCollector::SCAVENGER && cpp_heap()) {
+  // Schedule Oilpan's Minor GC. Since the minor GC doesn't support conservative
+  // stack scanning, do it only when Scavenger runs from task, which is
+  // non-nestable.
+  if (cpp_heap() && collector == GarbageCollector::SCAVENGER &&
+      gc_reason == GarbageCollectionReason::kTask) {
     CppHeap::From(cpp_heap())->RunMinorGC();
   }
 

src/heap/scavenge-job.cc

@@ -43,8 +43,11 @@ void ScavengeJob::ScheduleTaskIfNeeded(Heap* heap) {
     v8::Isolate* isolate = reinterpret_cast<v8::Isolate*>(heap->isolate());
     auto taskrunner =
         V8::GetCurrentPlatform()->GetForegroundTaskRunner(isolate);
-    taskrunner->PostTask(std::make_unique<Task>(heap->isolate(), this));
-    task_pending_ = true;
+    if (taskrunner->NonNestableTasksEnabled()) {
+      taskrunner->PostNonNestableTask(
+          std::make_unique<Task>(heap->isolate(), this));
+      task_pending_ = true;
+    }
   }
 }