Add iron-list to polymer_resources.grdp
Add iron-list to polymer_resources.grdp

Will be used in MD Settings languages page, among others.

Review URL: https://codereview.chromium.org/1365573002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#350473}

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