[heap] Create a thin wrapper around wrapper tracing in V8 to avoid misuse

src/heap/embedder-tracing.h

+// Copyright 2016 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.
+
+#ifndef V8_HEAP_EMBEDDER_TRACING_H_
+#define V8_HEAP_EMBEDDER_TRACING_H_
+
+#include "include/v8.h"
+#include "src/globals.h"
+
+namespace v8 {
+namespace internal {
+
+class Heap;
+
+class V8_EXPORT_PRIVATE LocalEmbedderHeapTracer final {
+ public:
+  typedef std::pair<void*, void*> WrapperInfo;
+
+  LocalEmbedderHeapTracer() : remote_tracer_(nullptr) {}
+
+  void SetRemoteTracer(EmbedderHeapTracer* tracer) { remote_tracer_ = tracer; }
+  bool InUse() { return remote_tracer_ != nullptr; }
+
+  void TracePrologue();
+  void TraceEpilogue();
+  void AbortTracing();
+  void EnterFinalPause();
+  bool Trace(double deadline,
+             EmbedderHeapTracer::AdvanceTracingActions actions);
+
+  size_t NumberOfWrappersToTrace();
+  size_t NumberOfCachedWrappersToTrace() {
+    return cached_wrappers_to_trace_.size();
+  }
+  void AddWrapperToTrace(WrapperInfo entry) {
+    cached_wrappers_to_trace_.push_back(entry);
+  }
+  void ClearCachedWrappersToTrace() { cached_wrappers_to_trace_.clear(); }
+  void RegisterWrappersWithRemoteTracer();
+
+  // In order to avoid running out of memory we force tracing wrappers if there
+  // are too many of them.
+  bool RequiresImmediateWrapperProcessing();
+
+ private:
+  typedef std::vector<WrapperInfo> WrapperCache;
+
+  EmbedderHeapTracer* remote_tracer_;
+  WrapperCache cached_wrappers_to_trace_;
+};
+
+}  // namespace internal
+}  // namespace v8
+
+#endif  // V8_HEAP_EMBEDDER_TRACING_H_