[Bindings] Create and use V8 context snapshots

third_party/WebKit/Source/bindings/core/v8/V8ContextSnapshot.h

+// Copyright 2017 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 V8ContextSnapshot_h
+#define V8ContextSnapshot_h
+
+#include "core/CoreExport.h"
+#include "platform/wtf/Allocator.h"
+#include "v8/include/v8.h"
+
+namespace blink {
+
+class Document;
+class DOMWrapperWorld;
+
+// This class contains helper functions to take and use a V8 context snapshot.

[haraken, 2017/07/10 06:52:08]

Explain how the V8 context snapshot works. In particular:

- The context snapshot is taken by tools/v8_context_snapshot/ when Chromium is
built.

- The context snapshot is used when Blink creates a new V8 context.

- The context snapshot contains:
--- Interface templates of Window, Node, Document and HTMLDocument.
--- Internal fields of wrappers of Window, Node, Document and HTMLDocument.
--- References of C++ callbacks exposed to V8.
--- window.document (only for the main world).
--- anything else?

- The context snapshot supports only the main thread. If it is the main world,
we need a special logic to serialize / deserialize window.document (so only
HTMLDocument is supported on the main world). Worker threads are not yet
supported.

[peria, 2017/07/10 10:18:43]

Done.

+class CORE_EXPORT V8ContextSnapshot {
+  STATIC_ONLY(V8ContextSnapshot);
+
+ public:
+  static v8::Local<v8::Context> CreateContextFromSnapshot(
+      v8::Isolate*,
+      const DOMWrapperWorld&,
+      v8::ExtensionConfiguration*,
+      v8::Local<v8::Object> global_proxy,
+      Document*);
+  // Install runtime enabled features on some v8::Object's in a context
+  // created from a snapshot.
+  static void InstallRuntimeEnabledFeatures(v8::Local<v8::Context>, Document*);
+
+  static void EnsureInterfaceTemplates(v8::Isolate*);
+
+  static void SetReferenceTable(intptr_t* table);
+  static intptr_t* GetReferenceTable();
+
+  // Do not call this in production.
+  static v8::StartupData TakeSnapshot();
+
+ private:
+  static v8::StartupData SerializeInternalField(v8::Local<v8::Object> holder,
+                                                int index,
+                                                void* data);
+  static void DeserializeInternalField(v8::Local<v8::Object> holder,
+                                       int index,
+                                       v8::StartupData payload,
+                                       void* data);
+  static bool CanCreateContextFromSnapshot(v8::Isolate*,
+                                           const DOMWrapperWorld&,
+                                           Document*);
+
+  static void EnsureInterfaceTemplatesForWorld(v8::Isolate*,
+                                               const DOMWrapperWorld&);
+
+  static void TakeSnapshotForWorld(v8::SnapshotCreator*,
+                                   const DOMWrapperWorld&);
+};
+
+}  // namespace blink
+
+#endif  // V8ContextSnapshot_h