Bikeshed changing default chrome flags used.

Breaking this out from #38 where we explored this the most. cc @ragingwind

Here is the node module API implemented in #38 (let’s call this JS vAlpha API):

chromeLauncher.defaultFlags() // array of all the flags it uses by default

chromeLauncher.launch({
  ignoreDefaultFlags: true,  // will not supply any defaults.. the ones passed in below are it.
  chromeFlags: [] // array of the only flags to use
});

and a CLI vAlpha API:

chrome-launcher --list-flags # prints and quits: '--disable-extensions --disable-translate-service ....'

chrome-launcher # launches with default flags
chrome-launcher --set-flags="--show-paint-rects --disable-extensions"   # skips default flags and only uses provided ones
# naming: maybe "override-flags" to indicate this may break things..

# also allow just augmenting default flags with --add-flags
chrome-launcher --add-flags="--show-paint-rects"
# (this behavior is what lighthouse's current --chrome-flags arg does)

[patrickhulce]

Yes @Gudahtt I believe we consider this resolved by https://github.com/GoogleChrome/chrome-launcher/pull/124. We can revisit a future date if there becomes a stronger need for a CLI.

[paulirish]

As discussed with @patrickhulce here’s a JS vGamma API:

const flags = chromeLauncher.defaultFlags() // Map of all the flags it uses by default

flags.delete('--disable-extensions');
flags.delete('--mute-audio');
flags.set('--user-data-dir', somepath);

chromeLauncher.launch({chromeFlags: flags});

And we’d use a little duck typing:

• If chromeFlags is an array, add the results on to the default flags.
• If chromeFlags is a map, do not apply default flags and only use the provided ones (plus remote-debugging-port).

(While this has a very different API than the CLI, it kinda makes sense that they do.)