Same-document navigation follows a different code path than normal navigation
and was therefore not covered in the initial implementation for text fragments.
Same-document navigation does not set a URI in the `Document`, which
is the way cross-document navigation would parse text directives from the URL.
Instead, `nsDocShell::ScrollToAnchor()` is called via
`nsDocShell::InternalLoad()`-> `nsDocShell::HandleSameDocumentNavigation()`.
This code path needs to parse and remove the fragment directive from the new
fragment to be able to find text fragments and to allow for element-id fallback.
`nsDocShell::ScrollToAnchor()` needs to start an attempt to scroll to the text fragment
if it exists. It must not, however, clear the uninvoked text directives, because a
same-document navigation could happen before the document is fully loaded,
hence the target text might not be part of the DOM tree.
As per spec, a second attempt to scroll to the text fragment is done after the load
is completed. This is done by `Document::ScrollToRef()`, which is called by
`nsDocumentViewer::LoadComplete()` after the load has finished.
This call will clear the uninvoked directives.
Differential Revision: https://phabricator.services.mozilla.com/D209726
Jan-Niklas Jaeschke
b78b4a3fe3