[wrapper-tracing] Bring remoteplayback up to date

third_party/WebKit/Source/bindings/templates/callback_function.cpp.tmpl

Index: third_party/WebKit/Source/bindings/templates/callback_function.cpp.tmpl
diff --git a/third_party/WebKit/Source/bindings/templates/callback_function.cpp.tmpl b/third_party/WebKit/Source/bindings/templates/callback_function.cpp.tmpl
index ecf618e362ab4a4ebc7ca4369ceabf67c2288b65..d5c90f1200a685ff3962f989ab656d9f9c0efc5b 100644
--- a/third_party/WebKit/Source/bindings/templates/callback_function.cpp.tmpl
+++ b/third_party/WebKit/Source/bindings/templates/callback_function.cpp.tmpl
@@ -22,6 +22,11 @@ DEFINE_TRACE({{cpp_class}})
 {
 }
 
+DEFINE_TRACE_WRAPPERS({{cpp_class}})
+{
+    visitor->traceWrappers(&reinterpret_cast<ScopedPersistent<v8::Object>&>(const_cast<ScopedPersistent<v8::Function>&>(m_callback)));

[Marcel Hlopko, 2016/10/19 15:08:17]

Kentaro, just to be sure, should really each blink callback object keep its
wrapper alive?

[Michael Lippautz, 2016/10/19 15:13:41]

This infra merely adds the capability of blink callbacks keeping the wrapper
alive. You still require the parent object to call traceWrappers on the
callback, which only RemotePlayback currently does.

[haraken, 2016/10/19 15:31:43]

In almost all cases, the spec requires to add a strong reference from the
wrapper to the callback functions.

In any case, making the parent object explicitly call traceWrappers() sounds
like a good programming pattern. We can represent any reachability with it.

[haraken, 2016/10/19 15:31:43]

Can we add an overloaded function to traceWrappers() so that we don't need to
write complicated reinterpret_cast on the caller side?

[Michael Lippautz, 2016/10/19 15:44:34]

traceWrappers is overloaded with the two basic v8 type v8::Object and v8::Value.


I'd rather add a 
  template<typename S>
  const ScopedPersistent<S>& ScopedPersistent<T>::cast() const;
and use that one here.

[Michael Lippautz, 2016/10/19 15:44:35]

Acknowledged.

+}
+
 bool {{cpp_class}}::call({{argument_declarations | join(', ')}})
 {
     if (!scriptState->contextIsValid())