Only create RenderedDocumentMarkers for TextMatchMarkerListImpl

This sets us up to start creating a polymorphic class hierarchy for
DocumentMarker. RenderedDocumentMarker will become TextMatchMarker, and we will
also add subclasses of DocumentMarker for the other MarkerTypes as well.

BUG=715365

Review-Url: https://codereview.chromium.org/2883503004
Cr-Commit-Position: refs/heads/master@{#473345}
11 files changed