Introduce infrastructure for tracing ScriptWrappables.

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

Index: third_party/WebKit/Source/bindings/core/v8/ScriptWrappableVisitor.h
diff --git a/third_party/WebKit/Source/bindings/core/v8/ScriptWrappableVisitor.h b/third_party/WebKit/Source/bindings/core/v8/ScriptWrappableVisitor.h
new file mode 100644
index 0000000000000000000000000000000000000000..d547df2a3b987626af26c595066048bf06ef298f
--- /dev/null
+++ b/third_party/WebKit/Source/bindings/core/v8/ScriptWrappableVisitor.h
@@ -0,0 +1,88 @@
+// Copyright 2016 The Chromium 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 ScriptWrappableVisitor_h
+#define ScriptWrappableVisitor_h
+
+#include "platform/heap/HeapAllocator.h"
+#include <v8.h>
+#include <vector>
+
+
+namespace blink {
+
+class HeapObjectHeader;
+class ScriptWrappable;
+class ScriptWrappableHeapTracer;
+class NodeRareData;
+
+/**
+ * Declares non-virtual traceWrappers method. Should be used on
+ * non-ScriptWrappable classes which should participate in wrapper tracing (e.g.
+ * NodeRareData):
+ *
+ *     class NodeRareData {
+ *     public:
+ *         DECLARE_NONVIRTUAL_TRACE_WRAPPERS();
+ *     }
+ */
+#define DECLARE_NONVIRTUAL_TRACE_WRAPPERS()                               \

[haraken, 2016/04/19 04:58:31]

DECLARE_NONVIRTUAL_TRACE_WRAPPERS => DECLARE_TRACE_WRAPPERS (to make the macro
consistent with Oilpan's one)

[Marcel Hlopko, 2016/04/19 12:40:30]

Done.

+    void traceWrappers(const ScriptWrappableVisitor*) const
+
+/**
+ * Declares virtual traceWrappers method. It is used in ScriptWrappable, and can
+ * be used by non-ScriptWrappable classes which expect being inherited.
+ */
+#define DECLARE_VIRTUAL_TRACE_WRAPPERS()                                  \
+    virtual DECLARE_NONVIRTUAL_TRACE_WRAPPERS()
+
+/**
+ * Declares overridden traceWrappers method in the subclass of a class with
+ * DECLARE_VIRTUAL_TRACE_WRAPPERS(), used e.g. in dom/Node:
+ *
+ *     class Node : public ScriptWrappable {
+ *          OVERRIDE_TRACE_WRAPPERS();
+ *     }
+ */
+#define OVERRIDE_TRACE_WRAPPERS()                                         \

[haraken, 2016/04/19 04:58:31]

Yeah, I'd prefer dropping OVERRIDE in order to make the macros consistent with
Oilpan's ones.

[Marcel Hlopko, 2016/04/19 12:40:30]

Done.

+    DECLARE_VIRTUAL_TRACE_WRAPPERS() override;
+
+/**
+ * Provides definition of traceWrappers method. Custom code will usually call
+ * visitor->traceWrappers with all objects which could contribute to the set of
+ * reachable wrappers:
+ *
+ *     DEFINE_TRACE_WRAPPERS(NodeRareData)
+ *     {
+ *         visitor->traceWrappers(m_nodeLists);
+ *         visitor->traceWrappers(m_mutationObserverData);
+ *     }
+ */
+#define DEFINE_TRACE_WRAPPERS(T)                                          \
+    void T::traceWrappers(const ScriptWrappableVisitor* visitor) const
+
+/**
+ * ScriptWrappableVisitor is able to trace through the script wrappable
+ * references. It is used by the ScriptWrappableHeapTracer during V8 garbage
+ * collection.
+ */
+class ScriptWrappableVisitor {

[haraken, 2016/04/19 04:58:31]

I guess you can just remove ScriptWrappableVisitor and move the contents to
ScriptWrappableHeapTracer. It looks redundant to create a new
ScriptWrappableVisitor every time you trace one ScriptWrappable object. You can
just use the ScriptWrappableHeapTracer (which is a singleton).

Nit: Then I'll rename ScriptWrappableHeapTracer to ScriptWrappableVisitor.

[Marcel Hlopko, 2016/04/19 12:40:30]

Done. I cleaned up v8 api once again.

+    STACK_ALLOCATED();
+public:
+    ScriptWrappableVisitor(v8::Isolate* isolate, ScriptWrappableHeapTracer* tracer)
+        : m_isolate(isolate)
+        , m_tracer(tracer)
+        {};
+    void traceWrappers(const ScriptWrappable* wrappable) const;
+    void traceWrappers(const ScriptWrappable& wrappable) const;
+private:
+    void markHeader(const ScriptWrappable* scriptWrappable) const;
+    void markHeader(const void* garbageCollected) const;
+    bool isHeaderMarked(const void* garbageCollected) const;
+    v8::Isolate* m_isolate;
+    ScriptWrappableHeapTracer* m_tracer;
+};
+
+}
+#endif