Starting with Chrome version 60, top-frame Urls have been blocked, as follows:
Summary
We intend to block web pages from loading data: Urls in the top frame using tags, window.open, window.Location and similar mechanisms.
Motivation
data: Urls are generally a source of Confusion for users. Because of their unfamiliarity and Ability to Encode arbitrary untrusted content in a URL, they are widely being used in spoofing and phishing Attacks. Another problem is that they can be passed along without a backing page that runs Javascript (e.g. a data URL can be sent via email). For that Reason, we intend to block top-frame navigations to data Urls.
Source: https://productforums.google.com/forum/#! topic/Chrome/k-9y57tme2E
Alternative:
Render your PDF in one <object>
var base64 = 'seuBase64';
var novaJanela = window.open("", "PDF", 'dependent=yes,locationbar=no,scrollbars=no,menubar=no,resizable,screenX=50,screenY=50,width=850,height=800');
novaJanela.document.write('<html><body><object width=100% height=100% type="application/pdf" data="data:application/pdf;base64,' + base64 + '"><embed type="application/pdf" src="data:application/pdf;base64,' + base64 + '"></embed></object></body></html>');
novaJanela.window.focus();