First implementation of lazily cached accessor for DOM attributes.

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 fd4b6d40407e7cca59400b8c1bdd1de35542a5f6..9ff5bd427f534b4d8cf74d2828d29c6af0939658 100644
--- a/third_party/WebKit/Source/bindings/IDLExtendedAttributes.md
+++ b/third_party/WebKit/Source/bindings/IDLExtendedAttributes.md
@@ -1484,7 +1484,7 @@ Summary: Caches the accessor result in a private property (not directly accesibl
 ***
 
 
-Usage: `[CachedAccessor]` takes no arguments, can be specified on attributes.
+Usage: `[CachedAccessor]` takes an optional argument "Lazy", can be specified on attributes.
 
 ```webidl
 interface HTMLFoo {
@@ -1492,6 +1492,11 @@ interface HTMLFoo {
 };
 ```
 
+```webidl
+interface HTMLFoo {
+    [CachedAccessor=Lazy] readonly attribute Bar bar;
+};
+```
 
 Register the required property in V8PrivateProperty.h.
 To update the cached value (e.g. for HTMLFoo.bar) proceed as follows: