[wrapper-tracing] Support for incrementally tracing ScopedPersistent

third_party/WebKit/Source/bindings/core/v8/ScopedPersistent.h

Index: third_party/WebKit/Source/bindings/core/v8/ScopedPersistent.h
diff --git a/third_party/WebKit/Source/bindings/core/v8/ScopedPersistent.h b/third_party/WebKit/Source/bindings/core/v8/ScopedPersistent.h
index 25333d7e640018e81a364407ee05d57f084327d6..844f5ba5057da806a31cba6e12e1da3a96d61fe0 100644
--- a/third_party/WebKit/Source/bindings/core/v8/ScopedPersistent.h
+++ b/third_party/WebKit/Source/bindings/core/v8/ScopedPersistent.h
@@ -31,6 +31,7 @@
 #ifndef ScopedPersistent_h
 #define ScopedPersistent_h
 
+#include "bindings/core/v8/ScriptWrappableVisitor.h"
 #include "wtf/Allocator.h"
 #include "wtf/Noncopyable.h"
 #include <memory>
@@ -55,7 +56,7 @@ class ScopedPersistent {
       m_handle.Reset(isolate, local);
   }
 
-  ~ScopedPersistent() { clear(); }
+  virtual ~ScopedPersistent() { clear(); }
 
   ALWAYS_INLINE v8::Local<T> newLocal(v8::Isolate* isolate) const {
     return v8::Local<T>::New(isolate, m_handle);
@@ -79,7 +80,7 @@ class ScopedPersistent {
   bool isEmpty() const { return m_handle.IsEmpty(); }
   bool isWeak() const { return m_handle.IsWeak(); }
 
-  void set(v8::Isolate* isolate, v8::Local<T> handle) {
+  virtual void set(v8::Isolate* isolate, v8::Local<T> handle) {
     m_handle.Reset(isolate, handle);
   }
 
@@ -112,6 +113,42 @@ class ScopedPersistent {
   v8::Persistent<T> m_handle;
 };
 
+/**
+ * TraceWrapperV8Reference is used to trace from Blink to V8.
+ *
+ * TODO(mlippautz): Once shipped, create a separate type with a more
+ * appropriate handle type than v8::Persistent. The handle should have regular
+ * tracing semantics, i.e., only hold strongly on to an object if reached
+ * through tracing.
+ */
+template <typename T>
+class TraceWrapperV8Reference : public ScopedPersistent<T> {
+ public:
+  explicit TraceWrapperV8Reference(void* parent)
+      : ScopedPersistent<T>(), m_parent(parent) {}
+
+  TraceWrapperV8Reference(v8::Isolate* isolate,
+                          void* parent,
+                          v8::Local<T> handle)
+      : ScopedPersistent<T>(isolate, handle), m_parent(parent) {
+    ScriptWrappableVisitor::writeBarrier(m_parent, &cast<v8::Value>());
+  }
+
+  void set(v8::Isolate* isolate, v8::Local<T> handle) override {
+    ScopedPersistent<T>::set(isolate, handle);
+    ScriptWrappableVisitor::writeBarrier(m_parent, &cast<v8::Value>());
+  }
+
+  template <typename S>
+  const TraceWrapperV8Reference<S>& cast() const {
+    return reinterpret_cast<const TraceWrapperV8Reference<S>&>(
+        const_cast<const TraceWrapperV8Reference<T>&>(*this));
+  }
+
+ private:
+  void* m_parent;
+};
+
 }  // namespace blink
 
 #endif  // ScopedPersistent_h