Rewrite loops in DocumentMarkerController to use ListForType()

xiaochengh pointed out in another code review that this method is not being used
consistently:
https://codereview.chromium.org/2820633002#msg26

After this CL, it will be used consistently.

BUG=707867

Review-Url: https://codereview.chromium.org/2830033002
Cr-Commit-Position: refs/heads/master@{#466290}
1 file changed