Make sure findDOMNode works on test renderer

[sophiebits]

This injection is missing in the stack test renderer:

react/src/renderers/dom/stack/client/ReactDOMStackInjection.js

Lines 69 to 72 in 2da35fc

	findDOMNode._injectStack(function(inst) {
	inst = getHostComponentFromComposite(inst);
	return inst ? ReactDOMComponentTree.getNodeFromInstance(inst) : null;
	});

Something similar should be added near here:

https://github.com/facebook/react/blob/master/src/renderers/testing/stack/ReactTestRendererStack.js#L136

Without that, you get a "Missing injection for stack findDOMNode" error when calling findDOMNode in files that use ReactTestRenderer (and don't use ReactDOM). Would be great to repro the error with a test and then fix it.

[sophiebits]

Hm, not sure this makes sense actually.

[sophiebits]

Gonna close this for now until I figure out what we actually want.

[aweary]

@spicyj there was some discussion in #8164 about why we weren't supporting findDOMNode in the test renderer

[sophiebits]

Good memory, thanks. :)