Control use of JavaScript JIT

Allows you to set whether Brave will run the v8 JavaScript engine with JIT (Just In Time) compiler enabled or not. Disabling the JavaScript JIT will mean that Brave may render web content more slowly, and may also disable parts of JavaScript including WebAssembly. Disabling the JavaScript JIT may allow Brave to render web content in a more secure configuration. This policy can be overridden for specific URL patterns using the JavaScriptJitAllowedForSites and JavaScriptJitBlockedForSites policies. If this policy is left not set, JavaScript JIT is enabled.