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

**What is the current behavior?**
I got this warning: `Warning: Extra attributes from the server: preserveAspectRatio,viewBox` during client side hydratation when my react tree contains mixed case attributes such as these svg ones.

**What is the expected behavior?**

No warnings because there are no difference between server and client attributes.

**Which versions of React, and which browser / OS are affected by this issue? Did this work in previous versions of React?**

**React 16.0.0-rc.2**
This worked on 15.*

This seems to happen because the attribute name is put to lowercase here: https://github.com/facebook/react/blob/6552519a211c3e43e3f6cf5b2237c90ae515d423/src/renderers/dom/fiber/ReactDOMFiberComponent.js#L901
but not in the set here:
https://github.com/facebook/react/blob/6552519a211c3e43e3f6cf5b2237c90ae515d423/src/renderers/dom/fiber/ReactDOMFiberComponent.js#L915
As the set removal is done with the lowercased attribute:
https://github.com/facebook/react/blob/6552519a211c3e43e3f6cf5b2237c90ae515d423/src/renderers/dom/fiber/ReactDOMFiberComponent.js#L1011
it stays in the `extraAttributeNames` set and I got wrongly the previous warning.
);
        expect(style.lineClamp).toBe('10');
        expect(style.WebkitLineClamp).toBe('10');
        expect(style.MozFlexGrow).toBe('10');
        
        
        
        expect(style.MsFlexGrow || style.msFlexGrow).toBe('10');
        expect(style.MsGridRow || style.msGridRow).toBe('10');
        expect(style.MsGridRowEnd || style.msGridRowEnd).toBe('10');
        expect(style.MsGridRowSpan || style.msGridRowSpan).toBe('10');
        expect(style.MsGridRowStart || style.msGridRowStart).toBe('10');
        expect(style.MsGridColumn || style.msGridColumn).toBe('10');
        expect(style.MsGridColumnEnd || style.msGridColumnEnd).toBe('10');
        expect(style.MsGridColumnSpan || style.msGridColumnSpan).toBe('10');
        expect(style.MsGridColumnStart || style.msGridColumnStart).toBe('10');
      });
    });
    describe('aria attributes', function() {
      itRenders('simple strings', async render => {
        const e = await render(<div aria-label="hello" />);
        expect(e.getAttribute('aria-label')).toBe('hello');
      });
      
      itRenders('aria string prop with false value', async render => {
        const e = await render(<div aria-label={false} />);
        expect(e.getAttribute('aria-label')).toBe('false');
      });
      itRenders('no aria prop with null value', async render => {
        const e = await render(<div aria-label={null} />);