[v8 gc] Introduce a base class for all objects that can have pending activity

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 46ace8a1985d35dcabcefe6e80535fc8e1567d75..b828ec2c08219580246b8e571bb70e8b978e2cf3 100644
--- a/third_party/WebKit/Source/bindings/IDLExtendedAttributes.md
+++ b/third_party/WebKit/Source/bindings/IDLExtendedAttributes.md
@@ -130,7 +130,7 @@ Extended attributes on members of an implemented interface work as normal. Howev
 
 ### Inheritance
 
-Extended attributes are generally not inherited: only extended attributes on the interface itself are consulted. However, there are a handful of extended attributes that are inherited (applying them to an ancestor interface applies them to the descendants). These are extended attributes that affect memory management, and currently consists of `[DependentLifetime]`; the up-to-date list is [compute_dependencies.INHERITED_EXTENDED_ATTRIBUTES](https://code.google.com/p/chromium/codesearch#chromium/src/third_party/WebKit/Source/bindings/scripts/compute_dependencies.py&q=INHERITED_EXTENDED_ATTRIBUTES).
+Extended attributes are generally not inherited: only extended attributes on the interface itself are consulted. However, there are a handful of extended attributes that are inherited (applying them to an ancestor interface applies them to the descendants). These are extended attributes that affect memory management, and currently consists of `[DependentLifetime]` and `[ActiveScriptWrappable]`; the up-to-date list is [compute_dependencies.INHERITED_EXTENDED_ATTRIBUTES](https://code.google.com/p/chromium/codesearch#chromium/src/third_party/WebKit/Source/bindings/scripts/compute_dependencies.py&q=INHERITED_EXTENDED_ATTRIBUTES).
 
 ## Standard Web IDL Extended Attributes
 
@@ -478,6 +478,40 @@ Usage: Can be specified on attributes or interfaces.
 
 These extended attributes are widely used.
 
+### [ActiveScriptWrappable] _(i)_
+
+Summary: `[ActiveScriptWrappable]` indicates that a given DOM object should be kept alive as long as the DOM object has pending activities.
+
+Usage: `[ActiveScriptWrappable]` can be specified on interfaces, and **is inherited**:
+
+```webidl
+[
+    ActiveScriptWrappable,
+] interface Foo {
+    ...
+};
+```
+
+If an interface X has `[ActiveScriptWrappable]` and an interface Y inherits the interface X, then the interface Y will also have `[ActiveScriptWrappable]`. For example
+
+```webidl
+[
+    ActiveScriptWrappable,
+] interface Foo {};
+```
+
+interface Bar : Foo {};  // inherits [ActiveScriptWrappable] from Foo
+If a given DOM object needs to be kept alive as long as the DOM object has pending activities, you need to specify `[ActiveScriptWrappable]` and `[DependentLifetime]`. For example, `[ActiveScriptWrappable]` can be used when the DOM object is expecting events to be raised in the future.
+
+If you use `[ActiveScriptWrappable]`, the corresponding Blink class needs to inherit ActiveScriptWrappable. For example, in case of XMLHttpRequest, core/xml/XMLHttpRequest.h would look like this:
+
+```c++
+class XMLHttpRequest : public ActiveScriptWrappable
+{
+    ...;
+}
+```
+
 ### [PerWorldBindings] _(m, a)_
 
 Summary: Generates faster bindings code by avoiding check for isMainWorld().
@@ -868,7 +902,7 @@ interface Bar : Foo { ... };  // inherits [DependentLifetime]
 If a DOM object does not have `[DependentLifetime]`, V8's GC collects the wrapper of the DOM object
 if the wrapper is unreachable on the JS side (i.e., V8's GC assumes that the wrapper should not be
 reachable in the DOM side). Use `[DependentLifetime]` to relax the assumption.
-For example, if the DOM object implements hasPendingActivity(), it must be annotated with
+For example, if the DOM object has `[ActiveScriptWrappable]` and implements hasPendingActivity(), it must be annotated with
 `[DependentLifetime]`. Otherwise, the wrapper will be collected regardless of the returned value
 of the hasPendingActivity(). DOM objects that are pointed to by `[SetWrapperReferenceFrom]` and
 `[SetWrapperReferenceTo]` must be annotated with `[DependentLifetime]`.