Saw this on ToT chrome (r523111), (and 65.0.3287.0/10209.0.0 dev channel, see https://bugs.chromium.org/p/chromium/issues/detail?id=777755#c13), while looking at issue 777755.

Repro:
1. Install hangouts app
   https://chrome.google.com/webstore/detail/google-hangouts/knipolnnllmklapflnccelgolnpehhpl
2. Launch the app and see its main UI window

At step 2, the window stays blank.

Might be related to recent <webview>, OOPIF work. The app window hosts the hangouts UI in a webview. When it happens, I saw the following errors:

[49765:49765:1213/105910.317699:INFO:CONSOLE(1)] "Uncaught TypeError: callbackWindow._GC_OnFrameReady is not a function", source: https://hangouts.google.com/webchat/u/0/frame2?v=1512768735&pvt=AMP3uWZazpy2fJilJySZJDAuGmQb717O2D6YpyqGtsrabD2tNLGbZlGC2hEOmivgPLNs_P3USK1B&prop=ChromeApp&hl=en_GB (1)
[49765:49765:1213/105910.399562:INFO:CONSOLE(93)] "<webview>: A new window was blocked.", source: extensions::webViewActionRequests (93)


It seems that the JS inside the <webview> tries to call window.open [1], which is blocked on ToT now and causing the JS error.

[1]: https://cs.corp.google.com/piper///depot/google3/java/com/google/buzz/webconnection/templates/FrameHtml.soy?rcl=170456968&l=42