Added property renderedHtml to return gen func

[justin808]

This is to support React Router v4, which needs the result of calling
renderToString.

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This change is 

[justin808]

@robwise @alexfedoseev can I get a quick review on the JS parts?
@mapreal19 @samnang please take a quick peek at the Ruby code.

[coveralls]

Coverage remained the same at 99.321% when pulling b719cb6 on justin800/allow-router-result-to-return-html-string into 53af841 on master.

[coveralls]

Coverage remained the same at 99.321% when pulling b719cb6 on justin800/allow-router-result-to-return-html-string into 53af841 on master.

[coveralls]

Coverage remained the same at 99.321% when pulling b719cb6 on justin800/allow-router-result-to-return-html-string into 53af841 on master.

[coveralls]

Coverage increased (+0.008%) to 99.329% when pulling 0512a2b on justin800/allow-router-result-to-return-html-string into 53af841 on master.

[coveralls]

Coverage increased (+0.008%) to 99.329% when pulling 0512a2b on justin800/allow-router-result-to-return-html-string into 53af841 on master.

[samnang]

Do you prefer to call it subject instead of page? To me, page is more explicit and specific in this context.

[justin808]

I'm being consistent with other tests in this file.

[samnang]

Why do we have to check with the whole string here instead of putting assertion on what we want to verify each part.

[justin808]

Because this is in a script tag.

[mapreal19]

Reviewed 6 of 19 files at r1.
Review status: 6 of 18 files reviewed at latest revision, 2 unresolved discussions.

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Comments from Reviewable

[coveralls]

Coverage remained the same at 99.329% when pulling 4cf969a on justin800/allow-router-result-to-return-html-string into 4e567a3 on master.

[coveralls]

Coverage remained the same at 99.329% when pulling 4cf969a on justin800/allow-router-result-to-return-html-string into 4e567a3 on master.

[alex35mil]

@justin808 I tried only client part of react-router@4 yet. Looking at docs for server rendering, api seems kinda strange, I don't get why 404 case requires second render. But anyway, talking about integration w/ react_on_rails— it LGTM.