Extension causes high cpu load

[AbhiAbzs]

• Issue Type: Performance
• Extension Name: html-css-class-completion
• Extension Version: 1.18.0
• OS Version: Linux x64 4.15.0-45-generic
• VSCode version: 1.31.0

Zignd.html-css-class-completion-unresponsive.cpuprofile.txt

[zignd]

Similar reports with attached .cpuprofile.txt files or better descriptions on the issue: #175, #180, #181, #207, #213, #214