This is part or RFC 5280 (Section 4.2.1.11), and is required in order to be compliant with RFC 5280's profile:
At a minimum, applications conforming to this profile MUST recognize
the following extensions: .... policy constraints (Section 4.2.1.11)
In practice I do not believe it is widely used in Web PKI. According to RFC 5280 it should be marked as critical.
Comment 1 by bugdroid1@chromium.org
, May 13 2017