Fixes styling (e.g. shadow, elevation) issues in Edge 40

[microDimensions]

Fixes PolymerElements/paper-styles#145, see also PolymerElements/paper-listbox#39

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[microDimensions]

I signed it!

[feuerste]

@e111077, what do you think about this PR? Adding a type doesn't hurt, but fixes a nasty Edge 40 styling bug, PolymerElements/paper-styles#145. Thanks for looking into it!

[e111077]

No problem at all