[MD settings] change dropdown to accept array of objects rather than array of tuples
This is an optional CL. There was a question from Micael about using named keys
for the menu options rather than an array index. This CL shows what that would
look like.
Performance side-effect: inconsequential (measured by hand).
BUG=
531786
Committed:
https://crrev.com/8bea8800993569264106223337a53ec02001b342
Cr-Commit-Position: refs/heads/master@{#361390}