Add [CachedAccessor] attribute to cache (almost) constant accessors (window.document).

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 1555 matching lines @@
     v8::FunctionCallback callback)
 {
   v8::experimental::FastAccessorBuilder* fab =
           v8::experimental::FastAccessorBuilder::New(isolate);
   fab->ReturnValue(fab->IntegerContant(123));
   return fab;
 }
 
 ```
 
+
+### [StoreInField] _(a)_

[haraken, 2016/09/15 09:26:10]

[CacheAttributeGetterResult] ?

(Given that an extended attribute is a Blink thing, I want to name it from the
Blink perspective.)

+
+Summary: Caches invariable accessors to a private property. Private property name is automatically generated e.g. "Class#attribute".

[jochen (gone - plz use gerrit), 2016/09/15 08:20:51]

hum, that sounds like there'd be some automatic caching and invalidation going
on, but that's not the case, no?

+
+
+*** note
+Useful for performance critical scenarios, where the accessor does little or none computation at all (peek a field), removing the calling overhead.
+Calls to the getter will be translated into a faster property load.
+***
+
+Usage: `[StoreInField]` takes no arguments, can be specified on attributes.
+
+
 ## Discouraged Blink-specific IDL Extended Attributes
 
 These extended attributes are _discouraged_ - they are not deprecated, but they should be avoided and removed if possible.
 
 ### [DoNotCheckConstants] _(i)_
 
 Summary: `[DoNotCheckConstants]` indicates that constant values in an IDL file can be different from constant values in Blink implementation.
 
 Usage: `[DoNotCheckConstants]` can be specified on interfaces:
 
@@ skipping 63 matching lines @@
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 ***