Follow up from https://github.com/facebook/react/pull/11616.

Here's one I found. These two invariants:

https://github.com/facebook/react/blob/7e7127387ba64f57299eaff8656542cea6fb3a2d/packages/react-reconciler/src/ReactFiberClassComponent.js#L330-L343

are in a function that's behind a DEV block:

https://github.com/facebook/react/blob/7e7127387ba64f57299eaff8656542cea6fb3a2d/packages/react-reconciler/src/ReactFiberClassComponent.js#L447-L449

I don't think this is intentional, but need to verify.

There may be more. I'll use this issue to track while https://github.com/facebook/react/pull/11616 preserves existing behavior.
expect(e.namespaceURI).toBe('http:www.w3.org/2000/svg');
        expect(e.getAttribute('viewBox')).toBe('0 0 0 0');
      });
      itRenders(
        'svg child element with a namespace attribute',
        async render => {
          let e = await render(
            <svg>
              <image xlinkHref="http:i.imgur.com/w7GCRPb.png" />
            </svg>,
          );
          e = e.firstChild;
          expect(e.childNodes.length).toBe(0);
          expect(e.tagName).toBe('image');
          expect(e.namespaceURI).toBe('http:www.w3.org/2000/svg');
          expect(e.getAttributeNS('http:www.w3.org/1999/xlink', 'href')).toBe(
            'http:i.imgur.com/w7GCRPb.png',
          );
        },
      );
      itRenders('svg child element with a badly cased alias', async render => {
        let e = await render(
          <svg>
            <image xlinkhref="http:i.imgur.com/w7GCRPb.png" />
          </svg>,
          1,
        );
        e = e.firstChild;
        expect(e.hasAttributeNS('http:www.w3.org/1999/xlink', 'href')).toBe(
          false,