Add linkClickIntercepted to FrameElementDelegate

Expand the `FrameElementDelegate` interface to include a
`linkClickIntercepted` to match its existing
`formSubmissionIntercepted`, then replace a manual `setAttribute` and
`src` assignment with a delegation to the `FrameElementDelegate`
instance.

src/core/frames/frame_redirector.ts

@@ -31,8 +31,7 @@ export class FrameRedirector implements LinkInterceptorDelegate, FormInterceptor
   linkClickIntercepted(element: Element, url: string) {
     const frame = this.findFrameElement(element)
     if (frame) {
-      frame.setAttribute("reloadable", "")
-      frame.src = url
+      frame.delegate.linkClickIntercepted(element, url)
     }
   }
 

src/elements/frame_element.ts

@@ -9,6 +9,7 @@ export interface FrameElementDelegate {
   sourceURLChanged(): void
   disabledChanged(): void
   formSubmissionIntercepted(element: HTMLFormElement, submitter?: HTMLElement): void
+  linkClickIntercepted(element: Element, url: string): void
   loadResponse(response: FetchResponse): void
   isLoading: boolean
 }