Launch Chrome with --disable-renderer-backgrounding flag

[cexbrayat]

On macOS 10.12.4 and Chrome 58.0.3029, it appears that my test suite is slow down if Chrome is in the background. #64 should have fixed it a long ago, but a comment is mentioning the --disable-renderer-backgrounding flag, so I gave it a try, and it does fix my issue:

Before (Angular CLI project using Karma/Chrome):

05 05 2017 10:44:24.333:INFO [launcher]: Starting browser Chrome
05 05 2017 10:44:25.105:INFO [Chrome 58.0.3029 (Mac OS X 10.12.4)]: Connected on socket xKymjhyLh5832m9sAAAA with id 81470424
Chrome 58.0.3029 (Mac OS X 10.12.4): Executed 102 of 102 SUCCESS (5.512 secs / 5.473 secs)
Chrome 58.0.3029 (Mac OS X 10.12.4): Executed 102 of 102 SUCCESS (29.198 secs / 29.164 secs)
Chrome 58.0.3029 (Mac OS X 10.12.4): Executed 102 of 102 SUCCESS (27.1 secs / 26.266 secs)
Chrome 58.0.3029 (Mac OS X 10.12.4): Executed 102 of 102 SUCCESS (28.606 secs / 27.676 secs)

First run is fast, the following are really slow.

After, with this karma.conf.js using the --disable-renderer-backgrounding flag:

    customLaunchers: {
      chromeBackground: {
        base: 'Chrome',
        flags: ['--disable-renderer-backgrounding']
      }
    },
    browsers: ['chromeBackground'],

The tests run faster:

05 05 2017 10:42:54.681:INFO [Chrome 58.0.3029 (Mac OS X 10.12.4)]: Connected on socket cAPHozikOSfUEEnpAAAA with id 83636627
Chrome 58.0.3029 (Mac OS X 10.12.4): Executed 102 of 102 SUCCESS (5.666 secs / 5.628 secs)
Chrome 58.0.3029 (Mac OS X 10.12.4): Executed 102 of 102 SUCCESS (6.864 secs / 6.831 secs)
Chrome 58.0.3029 (Mac OS X 10.12.4): Executed 102 of 102 SUCCESS (7.129 secs / 7.109 secs)

This may be related to the Chrome issue https://bugs.chromium.org/p/chromium/issues/detail?id=605498#c1