Fix chrome://device-emulator power settings

The dom-repeat element needs a two-way data binding (not just the
sub-item).

See https://github.com/Polymer/old-docs-site/issues/1461

Bug: 927517
Change-Id: I89bfc13b95eaaa64e3e0fc89ce60fe085040cb54
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1517163
Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Commit-Queue: Evan Stade <estade@chromium.org>
Cr-Commit-Position: refs/heads/master@{#640013}
2 files changed