remove redundant code in sourcedialog plugin
Changelog entry.
Merge branch 't/11290'
Initial code style fixes.
Extract core of iframe autogrow algorithm to a separate function.
Cache scrollable element and marker in a closure and refresh on contentDom.
It didn't make any sense.
Not needed any more.
Don't check that twice in a row.
Minor simplification.
Don't need to pass arguments and return values any more.
Find config values once.
Cache document and marker container.
First compare fast accessible values.
Reset overflow-y style when maximizing, so scrollbar is restored.
Remove unnecessary functions.
If max height is not limited, remove scroll before resizing editor, so we'll need one check only and there won't be editable width changes and blinking scroll.
Changelog entry.
Merge branch 't/11097'
Chrome needs some help selecting page breaks too.

Firefox seems to be able to select them without problems.  I don't
have IE to test with.