fix(drawer): Fix exports and closure tests

[kfranqueiro]

First of all, thanks so much @trimox for spotting this in #3422 before we even released!

This builds off of #3422 to fix closure tests, and also fix unit tests to reference mocks where needed.

[googlebot]

So there's good news and bad news.

👍 The good news is that everyone that needs to sign a CLA (the pull request submitter and all commit authors) have done so. Everything is all good there.

😕 The bad news is that it appears that one or more commits were authored or co-authored by someone other than the pull request submitter. We need to confirm that all authors are ok with their commits being contributed to this project. Please have them confirm that here in the pull request.

Note to project maintainer: This is a terminal state, meaning the cla/google commit status will not change from this state. It's up to you to confirm consent of all the commit author(s), set the cla label to yes (if enabled on your project), and then merge this pull request when appropriate.

[kfranqueiro]

@trimox can you give an OK in this PR since I based the branch off of your commits from #3422? Thanks!

[mdc-web-bot]

All 349 screenshot tests passed for commit a3adf0b vs. master! 💯🎉

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@3aa211d). Click here to learn what that means.
The diff coverage is 86.66%.

@@           Coverage Diff            @@
##             master   #3424   +/-   ##
========================================
  Coverage          ?   98.3%           
========================================
  Files             ?     119           
  Lines             ?    5017           
  Branches          ?     613           
========================================
  Hits              ?    4932           
  Misses            ?      85           
  Partials          ?       0

Impacted Files	Coverage Δ
packages/mdc-drawer/util.js	100% <100%> (ø)
packages/mdc-drawer/index.js	97.05% <85.71%> (ø)

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[trimox]

OK by me. 👍

[googlebot]

A Googler has manually verified that the CLAs look good.

(Googler, please make sure the reason for overriding the CLA status is clearly documented in these comments.)