Split custom element script use and move it into bindings

third_party/WebKit/Source/bindings/core/v8/ScriptCustomElementDefinition.cpp

+// 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.
+
+#include "bindings/core/v8/ScriptCustomElementDefinition.h"
+
+#include "bindings/core/v8/ScriptState.h"
+#include "bindings/core/v8/V8Binding.h"
+#include "bindings/core/v8/V8CustomElementsRegistry.h"
+#include "bindings/core/v8/V8HiddenValue.h"
+#include "wtf/Allocator.h"
+
+namespace blink {
+
+// Retrieves the custom elements constructor -> name map, creating it
+// if necessary. The same map is used to keep prototypes alive.
+static v8::Local<v8::Map> ensureCustomElementsRegistryMap(
+    ScriptState* scriptState,
+    CustomElementsRegistry* registry)
+{
+    CHECK(scriptState->world().isMainWorld());
+    v8::Local<v8::String> name = V8HiddenValue::customElementsRegistryMap(
+        scriptState->isolate());
+    v8::Local<v8::Object> wrapper =
+        toV8(registry, scriptState).As<v8::Object>();
+    v8::Local<v8::Value> map =
+        V8HiddenValue::getHiddenValue(scriptState, wrapper, name);
+    if (map.IsEmpty()) {
+        map = v8::Map::New(scriptState->isolate());
+        V8HiddenValue::setHiddenValue(scriptState, wrapper, name, map);
+    }
+    return map.As<v8::Map>();
+}
+
+ScriptCustomElementDefinition* ScriptCustomElementDefinition::forConstructor(
+    ScriptState* scriptState,
+    CustomElementsRegistry* registry,
+    const v8::Local<v8::Value>& constructor)
+{
+    if (!scriptState->contextIsValid())

[haraken, 2016/05/28 08:29:48]

Nit: I'd remove this check.

We normally don't check scriptState->contextIsValid() when the C++ method is
being called by JS (which means that you have a valid scriptState). We only
check it when the C++ method is invoked asynchronously by DOM (e.g., event
listeners).

You're right in that even if the C++ method is called by JS (and thus it's
guaranteed that you have a valid scriptState at the point when the C++ method is
invoked), the scriptState can go invalid when you call some V8 API (e.g.,
Get()). However, we don't check it every time for the following (subtle)
reasons:

- You need to check it every time you call V8 APIs on stack. This messes up the
code base and slows down performance.

- The spec does not have a concept of scriptState->contextIsValid(). Per the
spec, scriptState must be valid as long as you have any reference to the
browsing context. So ideally, we should remove scriptState->contextIsValid()
entirely.

- Lifetime management around scriptState->contextIsValid() is already broken in
many ways in other browsers as well.

+        return nullptr;
+    v8::Local<v8::Map> map =
+        ensureCustomElementsRegistryMap(scriptState, registry);
+    v8::Local<v8::Value> nameValue = v8CallOrCrash(
+        map->Get(scriptState->context(), constructor));
+    if (!nameValue->IsString())
+        return nullptr;
+    AtomicString name = toCoreAtomicString(nameValue.As<v8::String>());
+
+    // This downcast is safe because only
+    // ScriptCustomElementDefinitions have a name associated with a V8
+    // constructor in the map; see
+    // ScriptCustomElementDefinition::create. This relies on three
+    // things:
+    //
+    // 1. Only ScriptCustomElementDefinition adds entries to the map.
+    //    Audit the use of V8HiddenValue/hidden values in general and
+    //    how the map is handled--it should never be leaked to script.
+    //
+    // 2. CustomElementsRegistry does not overwrite definitions with a
+    //    given name--see the CHECK in CustomElementsRegistry::define
+    //    --and adds ScriptCustomElementDefinitions to the map without
+    //    fail.
+    //
+    // 3. The relationship between the CustomElementsRegistry and its
+    //    map is never mixed up; this is guaranteed by the bindings
+    //    system which provides a stable wrapper, and the map hangs
+    //    off the wrapper.
+    //
+    // At a meta-level, this downcast is safe because there is
+    // currently only one implementation of CustomElementDefinition in
+    // product code and that is ScriptCustomElementDefinition. But
+    // that may change in the future.
+    CustomElementDefinition* definition = registry->definitionForName(name);
+    CHECK(definition);
+    return static_cast<ScriptCustomElementDefinition*>(definition);
+}
+
+ScriptCustomElementDefinition* ScriptCustomElementDefinition::create(
+    ScriptState* scriptState,
+    CustomElementsRegistry* registry,
+    const CustomElementDescriptor& descriptor,
+    const v8::Local<v8::Object>& constructor,
+    const v8::Local<v8::Object>& prototype)
+{
+    ScriptCustomElementDefinition* definition =
+        new ScriptCustomElementDefinition(
+            scriptState,
+            descriptor,
+            constructor,
+            prototype);
+
+    // Add a constructor -> name mapping to the registry.
+    v8::Local<v8::Value> nameValue =
+        v8String(scriptState->isolate(), descriptor.name());
+    v8::Local<v8::Map> map =
+        ensureCustomElementsRegistryMap(scriptState, registry);
+    v8CallOrCrash(map->Set(scriptState->context(), constructor, nameValue));
+    // We add the prototype here to keep it alive; we make it a value
+    // not a key so authors cannot return another constructor as a
+    // prototype to overwrite a constructor in this map. We use the
+    // name because it is unique per-registry.
+    v8CallOrCrash(map->Set(scriptState->context(), nameValue, prototype));
+
+    return definition;
+}
+
+ScriptCustomElementDefinition::ScriptCustomElementDefinition(
+    ScriptState* scriptState,
+    const CustomElementDescriptor& descriptor,
+    const v8::Local<v8::Object>& constructor,
+    const v8::Local<v8::Object>& prototype)
+    : CustomElementDefinition(descriptor)
+    , m_constructor(scriptState->isolate(), constructor)
+    , m_prototype(scriptState->isolate(), prototype)
+{
+    // These objects are kept alive by references from the
+    // CustomElementsRegistry wrapper set up by
+    // ScriptCustomElementDefinition::create.
+    m_constructor.setPhantom();
+    m_prototype.setPhantom();
+}
+
+v8::Local<v8::Object> ScriptCustomElementDefinition::constructor(
+    ScriptState* scriptState) const
+{
+    DCHECK(!m_constructor.isEmpty());
+    return m_constructor.newLocal(scriptState->isolate());
+}
+
+v8::Local<v8::Object> ScriptCustomElementDefinition::prototype(
+    ScriptState* scriptState) const
+{
+    DCHECK(!m_prototype.isEmpty());
+    return m_prototype.newLocal(scriptState->isolate());
+}
+
+} // namespace blink