Remove SetWrapperReferenceTo and SetWrapperReferenceFrom

third_party/WebKit/Source/bindings/IDLExtendedAttributes.md

 # Blink IDL Extended Attributes
 
 [TOC]
 
 ## Introduction
 
 The main interest in extended attributes are their _semantics_: Blink implements many more extended attributes than the Web IDL standard, to specify various behavior.
 
 The authoritative list of allowed extended attributes and values is [bindings/IDLExtendedAttributes.txt](https://code.google.com/p/chromium/codesearch#chromium/src/third_party/WebKit/Source/bindings/IDLExtendedAttributes.txt). This is complete but not necessarily precise (there may be unused extended attributes or values), since validation is run on build, but coverage isn't checked.
 
@@ skipping 888 matching lines @@
 ] interface Foo { ... };
 
 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 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]`.
+of the hasPendingActivity().
 
 ### [DeprecateAs] _(m, a, c)_
 
 Summary: Measures usage of a deprecated feature via UseCounter, and notifies developers about deprecation via a console warning.
 
 `[DeprecateAs]` can be considered an extended form of `[MeasureAs]`: it both measures the feature's usage via the same UseCounter mechanism, and also sends out a warning to the console (optionally with a message) in order to inform developers that the code they've written will stop working at some point in the relatively near future.
 
 Usage: `[DeprecateAs]` can be specified on methods, attributes, and constants.
 
 ```webidl
@@ skipping 335 matching lines @@
 ```
 
 For more information, see [RuntimeEnabledFeatures](https://code.google.com/p/chromium/codesearch#chromium/src/third_party/WebKit/Source/platform/RuntimeEnabledFeatures.in).
 
 ### [SaveSameObject] _(a)_
 
 Summary: Caches the resulting object and always returns the same object.
 
 When specified, caches the resulting object and returns it in later calls so that the attribute always returns the same object. Must be accompanied with `[SameObject]`.
 
-### [SetWrapperReferenceFrom=xxx] _(i)_
-
-### [SetWrapperReferenceTo=xxx] _(i)_
-
-Summary: This generates code that allows you to set up implicit references between wrappers which can be used to keep wrappers alive during GC.
-
-Usage: `[SetWrapperReferenceFrom]` and `[SetWrapperReferenceTo]` can be specified on an interface. Use `[Custom=VisitDOMWrapper]` if want to write a custom function.
-
-```webidl
-[
-  SetWrapperReferenceFrom=element
-] interface XXX { ... };
-```
-
-The code generates a function called `XXX::visitDOMWrapper` which is called by `V8GCController` before GC. The function adds implicit references from the specified object to this object's wrapper to keep it alive.
-
-The `[SetWrapperReferenceFrom]` extended attribute takes a value, which is the function to call to get the object that determines whether the object is reachable or not. The currently valid values are: `document`, `element`, `owner`, `ownerNode`
-
-```webidl
-[
-  SetWrapperReferenceTo=targetMethod
-] interface YYY { ... };
-```
-
-The code generates a function called `YYY::visitDOMWrapper` which is called by `V8GCController` before GC. The function adds implicit references from this object's wrapper to a target object's wrapper to keeps it alive.
-
-The `[SetWrapperReferenceTo]` extended attribute takes a value, which is the method name to call to get the target object. For example, with the above declaration a call will be made to `YYY::targetMethod()` to get the target of the reference.
-
 ## Rare Blink-specific IDL Extended Attributes
 
 These extended attributes are rarely used, generally only in one or two places. These are often replacements for `[Custom]` bindings, and may be candidates for deprecation and removal.
 
 ### [CachedAttribute] _(a)_
 
 Summary: For performance optimization, `[CachedAttribute]` indicates that a wrapped object should be cached on a DOM object. Rarely used (only by IndexDB).
 
 Usage: `[CachedAttribute]` can be specified on attributes, and takes a required value, generally called is*Dirty (esp. isValueDirty):
 
@@ skipping 330 matching lines @@
 Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:
 
 1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
 
 2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.
 
 THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS “AS IS” AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 ***
 
 [CrossOriginProperties]: https://html.spec.whatwg.org/multipage/browsers.html#crossoriginproperties-(-o-)