WebUI: Update Polymer iron-fit-behavior version 1.2.5 -> 2.1.0.

Bug: 738611
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: I7b4dc9a517db2e0b7f0c632d918514ee74cecf02
Reviewed-on: https://chromium-review.googlesource.com/927682
Reviewed-by: Hector Carmona <hcarmona@chromium.org>
Commit-Queue: Demetrios Papadopoulos <dpapad@chromium.org>
Cr-Commit-Position: refs/heads/master@{#538299}
4 files changed