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diff --git a/devtools/shared/heapsnapshot/DeserializedNode.h b/devtools/shared/heapsnapshot/DeserializedNode.h
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+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2; -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_devtools_DeserializedNode__
+#define mozilla_devtools_DeserializedNode__
+
+#include <utility>
+
+#include "js/UbiNode.h"
+#include "js/UniquePtr.h"
+#include "mozilla/HashFunctions.h"
+#include "mozilla/Maybe.h"
+#include "mozilla/Vector.h"
+#include "mozilla/devtools/CoreDump.pb.h"
+
+// `Deserialized{Node,Edge}` translate protobuf messages from our core dump
+// format into structures we can rely upon for implementing `JS::ubi::Node`
+// specializations on top of. All of the properties of the protobuf messages are
+// optional for future compatibility, and this is the layer where we validate
+// that the properties that do actually exist in any given message fulfill our
+// semantic requirements.
+//
+// Both `DeserializedNode` and `DeserializedEdge` are always owned by a
+// `HeapSnapshot` instance, and their lifetimes must not extend after that of
+// their owning `HeapSnapshot`.
+
+namespace mozilla {
+namespace devtools {
+
+class HeapSnapshot;
+
+using NodeId = uint64_t;
+using StackFrameId = uint64_t;
+
+// A `DeserializedEdge` represents an edge in the heap graph pointing to the
+// node with id equal to `DeserializedEdge::referent` that we deserialized from
+// a core dump.
+struct DeserializedEdge {
+  NodeId referent;
+  // A borrowed reference to a string owned by this node's owning HeapSnapshot.
+  const char16_t* name;
+
+  explicit DeserializedEdge(NodeId referent, const char16_t* edgeName = nullptr)
+      : referent(referent), name(edgeName) {}
+  DeserializedEdge(DeserializedEdge&& rhs);
+  DeserializedEdge& operator=(DeserializedEdge&& rhs);
+
+ private:
+  DeserializedEdge(const DeserializedEdge&) = delete;
+  DeserializedEdge& operator=(const DeserializedEdge&) = delete;
+};
+
+// A `DeserializedNode` is a node in the heap graph that we deserialized from a
+// core dump.
+struct DeserializedNode {
+  using EdgeVector = Vector<DeserializedEdge>;
+  using UniqueStringPtr = UniquePtr<char16_t[]>;
+
+  NodeId id;
+  JS::ubi::CoarseType coarseType;
+  // A borrowed reference to a string owned by this node's owning HeapSnapshot.
+  const char16_t* typeName;
+  uint64_t size;
+  EdgeVector edges;
+  Maybe<StackFrameId> allocationStack;
+  // A borrowed reference to a string owned by this node's owning HeapSnapshot.
+  const char* jsObjectClassName;
+  // A borrowed reference to a string owned by this node's owning HeapSnapshot.
+  const char* scriptFilename;
+  // A borrowed reference to a string owned by this node's owning HeapSnapshot.
+  const char16_t* descriptiveTypeName;
+  // A weak pointer to this node's owning `HeapSnapshot`. Safe without
+  // AddRef'ing because this node's lifetime is equal to that of its owner.
+  HeapSnapshot* owner;
+
+  DeserializedNode(NodeId id, JS::ubi::CoarseType coarseType,
+                   const char16_t* typeName, uint64_t size, EdgeVector&& edges,
+                   const Maybe<StackFrameId>& allocationStack,
+                   const char* className, const char* filename,
+                   const char16_t* descriptiveName, HeapSnapshot& owner)
+      : id(id),
+        coarseType(coarseType),
+        typeName(typeName),
+        size(size),
+        edges(std::move(edges)),
+        allocationStack(allocationStack),
+        jsObjectClassName(className),
+        scriptFilename(filename),
+        descriptiveTypeName(descriptiveName),
+        owner(&owner) {}
+  virtual ~DeserializedNode() {}
+
+  DeserializedNode(DeserializedNode&& rhs)
+      : id(rhs.id),
+        coarseType(rhs.coarseType),
+        typeName(rhs.typeName),
+        size(rhs.size),
+        edges(std::move(rhs.edges)),
+        allocationStack(rhs.allocationStack),
+        jsObjectClassName(rhs.jsObjectClassName),
+        scriptFilename(rhs.scriptFilename),
+        descriptiveTypeName(rhs.descriptiveTypeName),
+        owner(rhs.owner) {}
+
+  DeserializedNode& operator=(DeserializedNode&& rhs) {
+    MOZ_ASSERT(&rhs != this);
+    this->~DeserializedNode();
+    new (this) DeserializedNode(std::move(rhs));
+    return *this;
+  }
+
+  // Get a borrowed reference to the given edge's referent. This method is
+  // virtual to provide a hook for gmock and gtest.
+  virtual JS::ubi::Node getEdgeReferent(const DeserializedEdge& edge);
+
+  struct HashPolicy;
+
+ protected:
+  // This is only for use with `MockDeserializedNode` in testing.
+  DeserializedNode(NodeId id, const char16_t* typeName, uint64_t size)
+      : id(id),
+        coarseType(JS::ubi::CoarseType::Other),
+        typeName(typeName),
+        size(size),
+        edges(),
+        allocationStack(Nothing()),
+        jsObjectClassName(nullptr),
+        scriptFilename(nullptr),
+        descriptiveTypeName(nullptr),
+        owner(nullptr) {}
+
+ private:
+  DeserializedNode(const DeserializedNode&) = delete;
+  DeserializedNode& operator=(const DeserializedNode&) = delete;
+};
+
+static inline js::HashNumber hashIdDerivedFromPtr(uint64_t id) {
+  return mozilla::HashGeneric(id);
+}
+
+struct DeserializedNode::HashPolicy {
+  using Lookup = NodeId;
+
+  static js::HashNumber hash(const Lookup& lookup) {
+    return hashIdDerivedFromPtr(lookup);
+  }
+
+  static bool match(const DeserializedNode& existing, const Lookup& lookup) {
+    return existing.id == lookup;
+  }
+};
+
+// A `DeserializedStackFrame` is a stack frame referred to by a thing in the
+// heap graph that we deserialized from a core dump.
+struct DeserializedStackFrame {
+  StackFrameId id;
+  Maybe<StackFrameId> parent;
+  uint32_t line;
+  uint32_t column;
+  // Borrowed references to strings owned by this DeserializedStackFrame's
+  // owning HeapSnapshot.
+  const char16_t* source;
+  const char16_t* functionDisplayName;
+  bool isSystem;
+  bool isSelfHosted;
+  // A weak pointer to this frame's owning `HeapSnapshot`. Safe without
+  // AddRef'ing because this frame's lifetime is equal to that of its owner.
+  HeapSnapshot* owner;
+
+  explicit DeserializedStackFrame(StackFrameId id,
+                                  const Maybe<StackFrameId>& parent,
+                                  uint32_t line, uint32_t column,
+                                  const char16_t* source,
+                                  const char16_t* functionDisplayName,
+                                  bool isSystem, bool isSelfHosted,
+                                  HeapSnapshot& owner)
+      : id(id),
+        parent(parent),
+        line(line),
+        column(column),
+        source(source),
+        functionDisplayName(functionDisplayName),
+        isSystem(isSystem),
+        isSelfHosted(isSelfHosted),
+        owner(&owner) {
+    MOZ_ASSERT(source);
+  }
+
+  JS::ubi::StackFrame getParentStackFrame() const;
+
+  struct HashPolicy;
+
+ protected:
+  // This is exposed only for MockDeserializedStackFrame in the gtests.
+  explicit DeserializedStackFrame()
+      : id(0),
+        parent(Nothing()),
+        line(0),
+        column(0),
+        source(nullptr),
+        functionDisplayName(nullptr),
+        isSystem(false),
+        isSelfHosted(false),
+        owner(nullptr){};
+};
+
+struct DeserializedStackFrame::HashPolicy {
+  using Lookup = StackFrameId;
+
+  static js::HashNumber hash(const Lookup& lookup) {
+    return hashIdDerivedFromPtr(lookup);
+  }
+
+  static bool match(const DeserializedStackFrame& existing,
+                    const Lookup& lookup) {
+    return existing.id == lookup;
+  }
+};
+
+}  // namespace devtools
+}  // namespace mozilla
+
+namespace JS {
+namespace ubi {
+
+using mozilla::devtools::DeserializedNode;
+using mozilla::devtools::DeserializedStackFrame;
+
+template <>
+class Concrete<DeserializedNode> : public Base {
+ protected:
+  explicit Concrete(DeserializedNode* ptr) : Base(ptr) {}
+  DeserializedNode& get() const { return *static_cast<DeserializedNode*>(ptr); }
+
+ public:
+  static void construct(void* storage, DeserializedNode* ptr) {
+    new (storage) Concrete(ptr);
+  }
+
+  CoarseType coarseType() const final { return get().coarseType; }
+  Id identifier() const override { return get().id; }
+  bool isLive() const override { return false; }
+  const char16_t* typeName() const override;
+  Node::Size size(mozilla::MallocSizeOf mallocSizeof) const override;
+  const char* jsObjectClassName() const override {
+    return get().jsObjectClassName;
+  }
+  const char* scriptFilename() const final { return get().scriptFilename; }
+  const char16_t* descriptiveTypeName() const override {
+    return get().descriptiveTypeName;
+  }
+
+  bool hasAllocationStack() const override {
+    return get().allocationStack.isSome();
+  }
+  StackFrame allocationStack() const override;
+
+  // We ignore the `bool wantNames` parameter because we can't control whether
+  // the core dump was serialized with edge names or not.
+  js::UniquePtr<EdgeRange> edges(JSContext* cx, bool) const override;
+
+  static const char16_t concreteTypeName[];
+};
+
+template <>
+class ConcreteStackFrame<DeserializedStackFrame> : public BaseStackFrame {
+ protected:
+  explicit ConcreteStackFrame(DeserializedStackFrame* ptr)
+      : BaseStackFrame(ptr) {}
+
+  DeserializedStackFrame& get() const {
+    return *static_cast<DeserializedStackFrame*>(ptr);
+  }
+
+ public:
+  static void construct(void* storage, DeserializedStackFrame* ptr) {
+    new (storage) ConcreteStackFrame(ptr);
+  }
+
+  uint64_t identifier() const override { return get().id; }
+  uint32_t line() const override { return get().line; }
+  uint32_t column() const override { return get().column; }
+  bool isSystem() const override { return get().isSystem; }
+  bool isSelfHosted(JSContext* cx) const override { return get().isSelfHosted; }
+  void trace(JSTracer* trc) override {}
+  AtomOrTwoByteChars source() const override {
+    return AtomOrTwoByteChars(get().source);
+  }
+  uint32_t sourceId() const override {
+    // Source IDs are local to their host process and are not serialized.
+    return 0;
+  }
+  AtomOrTwoByteChars functionDisplayName() const override {
+    return AtomOrTwoByteChars(get().functionDisplayName);
+  }
+
+  StackFrame parent() const override;
+  bool constructSavedFrameStack(
+      JSContext* cx, MutableHandleObject outSavedFrameStack) const override;
+};
+
+}  // namespace ubi
+}  // namespace JS
+
+#endif  // mozilla_devtools_DeserializedNode__