below is the code snippet to check the issue
----------------------
function testElementStyle(tag, id, property){
 		// test an element's style
		var docElement = document.documentElement;
		var testDiv = docElement.insertBefore(document.createElement(tag), docElement.firstChild);
		testDiv.id = id;
		var styleValue = (testDiv.currentStyle || getComputedStyle(testDiv, null))[property];
		docElement.removeChild(testDiv);
 		return styleValue;
 	} 
	
var parser = testElementStyle('x-parse', null, 'content');
console.log(parser);
------------------------

The new behavior was introduced in 11fb2ae26b6e84211adf8270eb4f0cf42b945fe8 (67.0.3365.0) and it correctly implements the specification. 

  Computed value on elements is by default 'normal'
  and on :before and :after computes to 'none'
  Spec: https://www.w3.org/TR/CSS2/generate.html#content

Able to reproduce the issue on Windows 10, mac 10.13.3 and Ubuntu 17.10 using chrome reported version #67.0.3396.62 and latest canary #69.0.3451.0.

This seems to be an intended behaviour as per comment #2 that was introduced in 11fb2ae26b6e84211adf8270eb4f0cf42b945fe8 (67.0.3365.0).
ccing ramya.v@ for further inputs on this issue.

Thanks...!!

Thanks all for the quick response.

Might be third party libraries might have designed based on the browser response for the earlier versions (seems to be other browsers didn't implement this way). I will also check if libraries have any update.

 Issue 849984  has been merged into this issue.