feat(checkbox): Added density mixin to checkbox

[abhiomkar]

Fixes #4885

[codecov-io]

Codecov Report

Merging #5016 into feature/density will not change coverage.
The diff coverage is n/a.

@@               Coverage Diff                @@
##           feature/density    #5016   +/-   ##
================================================
  Coverage            98.68%   98.68%           
================================================
  Files                  122      122           
  Lines                 5995     5995           
  Branches               791      791           
================================================
  Hits                  5916     5916           
  Misses                  78       78           
  Partials                 1        1

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[mdc-web-bot]

🤖 Beep boop!

Screenshot test report 🚦

3 screenshots changed from feature/density on commit a6aed5f:

• https://storage.googleapis.com/mdc-web-screenshot-tests/travis/2019/08/21/21_03_10_249/report/report.html?utm_source=github&utm_medium=pr_comment

Details

3 Added:

• spec/mdc-checkbox/mixins/density.html

[mdc-web-bot]

🤖 Beep boop!

Screenshot test report 🚦

3 screenshots changed from feature/density on commit eba295c:

• https://storage.googleapis.com/mdc-web-screenshot-tests/travis/2019/08/23/18_48_13_209/report/report.html?utm_source=github&utm_medium=pr_comment

Details

3 Added:

• spec/mdc-checkbox/mixins/density.html