Use visitDOMWrapper to preserve WebGL JS object wrappers

third_party/WebKit/Source/bindings/IDLExtendedAttributes.md

Index: third_party/WebKit/Source/bindings/IDLExtendedAttributes.md
diff --git a/third_party/WebKit/Source/bindings/IDLExtendedAttributes.md b/third_party/WebKit/Source/bindings/IDLExtendedAttributes.md
index ee6b3929762b256134611f623f1560dc4d00d493..3b1d4ca66c64ce039bfd049c53be877922973ae4 100644
--- a/third_party/WebKit/Source/bindings/IDLExtendedAttributes.md
+++ b/third_party/WebKit/Source/bindings/IDLExtendedAttributes.md
@@ -859,7 +859,31 @@ Usage:
 And then in V8XXXCustom.cpp:
 
 ```c++
-void V8XXX::visitDOMWrapper(DOMDataStore* store, void* object, v8::Persistent<v8::Object> wrapper)
+void V8XXX::visitDOMWrapper(v8::Isolate* isolate, ScriptWrappable* scriptWrappable, v8::Persistent<v8::Object> wrapper)
+{
+    ...
+}
+```
+
+
+#### [Custom=VisitDOMWrapperExtra] _(i)_

[haraken, 2016/08/31 23:14:50]

I do want to avoid introducing [Custom=VisitDOMWrapperExtra]. Would you
elaborate on why [Custom=VisitDOMWrapper] is not enough?

[Ken Russell (switch to Gerrit), 2016/09/01 00:08:49]

As mentioned in the summary below, these classes already use the extended IDL
attribute SetWrapperReferenceFrom, which generates a visitDOMWrapper. We don't
want to copy the autogenerated code into a custom visitDOMWrapper, in case the
bindings generator changes.

[Kai Ninomiya, 2016/09/02 18:29:22]

Done.

+
+Summary: Allows you to write extra custom code for visitDOMWrapper, without conflicting with the visitDOMWrapper implementation generated by `[SetWrapperReferenceFrom]`. That implementation will call your visitDOMWrapperExtra implementation. One use (WebGLRenderingContext.idl).
+
+Usage:
+
+```webidl
+[
+    Custom=VisitDOMWrapperExtra,
+] interface XXX {
+    ...
+};
+```
+
+And then in V8XXXCustom.cpp:
+
+```c++
+void V8XXX::visitDOMWrapperExtra(v8::Isolate* isolate, ScriptWrappable* scriptWrappable, v8::Persistent<v8::Object> wrapper)
 {
     ...
 }