Some devtools tests had been forced to run in e10s with just 1
content process in bug 1301340 and bug 1303113 because they were
failing.
Now there seems to have been enough e10s messaging fixes that these
tests work again. It seems safe to re-enable multi-content-processes
for them now.
MozReview-Commit-ID: ENfDdIXvIAI
Use ReactDOM.render instead of React.render (same for unmountComponentAtNode)
Update tests to observe both childList and characterData mutations when
expecting only text changes.
MozReview-Commit-ID: ILTgypkpZRz
