Update window.anonymous to window.isAnonymouslyFramed

As discussed in WICG/anonymous-iframe#1, we updated the name of the attribute to `window.isAnonymouslyFramed`.
TODO(lyf): update the image.

anonymous_iframes.md

@@ -2,7 +2,7 @@
 
 - **Author**: [email protected], [email protected]
 - **Created**: 2021-05-06
-- **Last Updated**: 2021-11-10
+- **Last Updated**: 2022-05-06
 
 ## Table of content
 - [A problem](#a-problem)
@@ -78,7 +78,7 @@ In parallel with the iframe attribute, we plan to add a new Fetch Metadata heade
 * `Sec-Fetch-COEP: credentialless`: the resource will be rendered in a context with a COEP of credentialless.
 * `Sec-Fetch-COEP: anonymous`: the resource will be rendered in an anonymous iframe.
 
-Additionally, we plan on adding a `window.anonymous` read-only attribute. By
+Additionally, we added a `window.isAnonymouslyFramed` read-only attribute. By
 default, this will return `false`. In anonymous iframes it will return `true`,
 allowing a document to check whether it was loaded in an anonymous iframe.
 
@@ -198,7 +198,7 @@ This solution runs into compatibility issues:
 
 #### What information might this feature expose to Web sites or other parties, and for what purposes is that exposure necessary?
 
-The `Sec-Fetch-COEP` header exposes the COEP of the environment a resource will be rendered in. This allows a server to decline answering a request if they do not want their resource to be embedded in a more dangerous environment. The `window.anonymous` method exposes whether a document is loaded in an anonymous iframe or not, allowing a document to change its behavior depending on the availability of existing credentials or stored resources.
+The `Sec-Fetch-COEP` header exposes the COEP of the environment a resource will be rendered in. This allows a server to decline answering a request if they do not want their resource to be embedded in a more dangerous environment. The `window.isAnonymouslyFramed` method exposes whether a document is loaded in an anonymous iframe or not, allowing a document to change its behavior depending on the availability of existing credentials or stored resources.
 
 #### Do features in your specification expose the minimum amount of information necessary to enable their intended uses?