DevTools: Show Source should point to `render`, not `constructor`

[theKashey]

Do you want to request a feature or report a bug?

Bug. Regression to be more concrete - facebook/react-devtools#1191

What is the current behavior?

Show Source points to a Function Component body, and Class Component constructor.

What is the expected behavior?

In both cases, you should see "render" methods, class constructor is never something you might want to jump straight into. It was working in this expected way in a previous version of Dev Tools.

Why this is an issue?

Well, until React-Hot-Loader is not 100% deprecated, "Show Source" would not work at all, as long as it (and not only it - mobx would do the same) is wrapping class constructor, however keeping render untouched.

[theKashey]

Basically this should be backported:

https://github.com/facebook/react-devtools/blob/v3.3.2/shells/webextension/src/panel.js#L73-L83

to here

react/packages/react-devtools-extensions/src/utils.js

Lines 16 to 19 in b438699

	chrome.devtools.inspectedWindow.eval(`
	if (window.$type != null) {
	inspect(window.$type);
	}

I hope this simplification was not intentional.

[bvaughn]

PRs are welcome.