child process not reaped

[takakawa]

when running in docker after a while, there are many many process left defunct

[ZekeLu]

see #752

You can do two things to make it better:

1. specify the init process to reap the zombie processes: https://docs.docker.com/engine/reference/run/#specify-an-init-process
2. try to use a single browser instance and create new tabs in it (instead of creating many browser instances)

chromedp/chromedp_test.go

Lines 112 to 113 in 40faabd

	// Same browser, new tab; not needing to start new chrome browsers for
	// each test gives a huge speed-up.

[ZekeLu]

Closing as a duplicate of #752