Introduce infrastructure for tracing ScriptWrappables.

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

+// 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 ScriptWrappableHeapTracer_h
+#define ScriptWrappableHeapTracer_h
+
+#include "bindings/core/v8/DOMWrapperWorld.h"
+#include <v8.h>
+#include <vector>
+
+namespace blink {
+
+class HeapObjectHeader;
+
+/**
+ * When this heap tracer is set to the v8::Isolate, the V8 will call it during

[Hannes Payer (out of office), 2016/04/19 07:44:33]

remove the in "the V8" also below and in other files.

[Marcel Hlopko, 2016/04/19 12:40:29]

Done.

+ * its garbage collection. At the beginning, it will call TraceRoots, then
+ * repeatedly (as v8 discovers more wrappers) it will call TraceWrappersFrom,
+ * and at the end it will call ClearTracingMarks.
+ */
+class ScriptWrappableHeapTracer : public v8::EmbedderHeapTracer {
+public:
+    ~ScriptWrappableHeapTracer() override;
+    void TracePrologue(v8::Isolate*) override;
+    void TraceWrappersFrom(v8::Isolate*, const std::vector<std::pair<void*, void*>>& internalFieldsOfPotentialWrappers) override;
+    void TraceWrappersFrom(v8::Isolate*, v8::Persistent<v8::Object>* wrapper);
+    void AddHeaderToUnmark(HeapObjectHeader*);

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

AddHeaderToUnmark => addHeaderToUnmark

[Marcel Hlopko, 2016/04/19 12:40:29]

Done.

+    void TraceEpilogue(v8::Isolate*) override;
+    /**
+     * Mark wrappers in all worlds for the given script wrappable as alive in
+     * the V8.
+     */
+    static void markWrappersInAllWorlds(const ScriptWrappable*, v8::Isolate*);
+    /**
+     * Mark given wrapper as alive in the V8.
+     */
+    static void markWrapper(const v8::Persistent<v8::Object>& handle, v8::Isolate*);
+private:
+    void TraceWrappersFrom(v8::Isolate*, std::pair<void*, void*> internalFields);

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

TraceWrappersFrom => traceWrappersFrom

[Marcel Hlopko, 2016/04/19 12:40:29]

Done.

+    bool m_tracingInProgress = false;
+    /**
+     * Collection of headers we need to unmark after the tracing finished. We
+     * assume it is safe to hold on to the headers because:
+     *     * oilpan objects cannot move
+     *     * objects this headers belong to are considered alive by the oilpan
+     *       gc (so they cannot be reclaimed). For the oilpan gc, wrappers are
+     *       part of the root set and wrapper will keep its ScriptWrappable
+     *       alive. Wrapper reachability is a subgraph of oilpan reachability,
+     *       therefore anything we find during tracing wrappers will be found by
+     *       oilpan gc too.
+     */
+    WTF::Vector<HeapObjectHeader*> m_headersToUnmark;
+};
+
+} // namespace blink
+
+#endif // ScriptWrappableHeapTracer_h