Problem/Motivation
drupal_html_class() is called often enough that it can benefit from static caching.
Proposed resolution
Add static caching to drupal_html_class().
Remaining tasks
Profiling
User interface changes
n/a
API changes
n/a
Related Issues
#1982018: [meta] Refactor template_preprocess()
#1757550: [meta] Convert core theme functions and templates to Twig