Explicitly open all files with utf-8 encoding in tools/polymer.py.

Bug: 1017874
Change-Id: I4c48c36574840b10b8a6ac0df4ce3e2643f13cd9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1881722
Commit-Queue: Sigurður Ásgeirsson <siggi@chromium.org>
Reviewed-by: Rebekah Potter <rbpotter@chromium.org>
Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Cr-Commit-Position: refs/heads/master@{#710312}
1 file changed