Force visibility-change checking in EditorView.

When an `EditorView` becomes attached, if hardware acceleration is enabled,
the call to `pollDOM` is a no-op because there's already a refresh pending.
This can cause problems, because then the initial measurements don't happen
and (for example) the lineHeight is left as null - it'll be set on the next
rendering, but not before subscribers to `workspaceView.eachEditorView` are
notified.
Merge pull request #3517 from smashwilson/ensure-measurements

Force visibility-change checking in EditorView's afterAttach method