Make DocumentMarkerController::Add[Spelling/Grammar]Marker() take EphemeralRange

Currently DocumentMarkerController::AddSpellingMarker() and AddGrammarMarker()
take two Positions (start and end). This CL changes them to instead take an
EphemeralRange for consistency with AddTextMatchMarker() and
AddCompositionMarker().

BUG=707867

Review-Url: https://codereview.chromium.org/2901213008
Cr-Commit-Position: refs/heads/master@{#475672}
6 files changed