Inputs should not mutate value on type conversion (#9806)

This is a follow-up on
https://github.com/facebook/react/pull/9584#discussion_r115642293. There
is no need to assign the value property of an input if the value
property of the React component changes types, but stringifies to the
same value. For example:

```javascript
DOM.render(<input value="true" />, el)
DOM.render(<input value={true} />, el)
```

In this case, the assignment to `input.value` will always be
cast to the string "true". There is no need to perform this
assignment. Particularly when we already cast the value to a string
later:

```javascript
// Cast `value` to a string to ensure the value is set correctly. While
// browsers typically do this as necessary, jsdom doesn't.
node.value = '' + value;
```

src/renderers/dom/client/wrappers/ReactDOMInput.js

@@ -226,7 +226,7 @@ var ReactDOMInput = {
           // browsers typically do this as necessary, jsdom doesn't.
           node.value = '' + value;
         }
-      } else if (node.value !== value) {
+      } else if (node.value !== '' + value) {
         // Cast `value` to a string to ensure the value is set correctly. While
         // browsers typically do this as necessary, jsdom doesn't.
         node.value = '' + value;

src/renderers/dom/client/wrappers/__tests__/ReactDOMInput-test.js

@@ -324,6 +324,46 @@ describe('ReactDOMInput', () => {
     expect(nodeValueSetter.mock.calls.length).toBe(1);
   });
 
+  it('should not incur unnecessary DOM mutations for numeric type conversion', () => {
+    var container = document.createElement('div');
+    ReactDOM.render(<input value="0" />, container);
+
+    var node = container.firstChild;
+    var nodeValue = '0';
+    var nodeValueSetter = jest.genMockFn();
+    Object.defineProperty(node, 'value', {
+      get: function() {
+        return nodeValue;
+      },
+      set: nodeValueSetter.mockImplementation(function(newValue) {
+        nodeValue = newValue;
+      }),
+    });
+
+    ReactDOM.render(<input value={0} />, container);
+    expect(nodeValueSetter.mock.calls.length).toBe(0);
+  });
+
+  it('should not incur unnecessary DOM mutations for the boolean type conversion', () => {
+    var container = document.createElement('div');
+    ReactDOM.render(<input value="true" />, container);
+
+    var node = container.firstChild;
+    var nodeValue = 'true';
+    var nodeValueSetter = jest.genMockFn();
+    Object.defineProperty(node, 'value', {
+      get: function() {
+        return nodeValue;
+      },
+      set: nodeValueSetter.mockImplementation(function(newValue) {
+        nodeValue = newValue;
+      }),
+    });
+
+    ReactDOM.render(<input value={true} />, container);
+    expect(nodeValueSetter.mock.calls.length).toBe(0);
+  });
+
   it('should properly control a value of number `0`', () => {
     var stub = <input type="text" value={0} onChange={emptyFunction} />;
     stub = ReactTestUtils.renderIntoDocument(stub);