Just ignore events on unmounted components

Fixes facebook#4865 and also seems to fixes facebook#3790.

src/renderers/dom/client/ReactMount.js

@@ -392,12 +392,11 @@ function findFirstReactDOMImpl(node) {
     do {
       lastID = internalGetID(current);
       current = current.parentNode;
-      invariant(
-        current != null,
-        'findFirstReactDOMImpl(...): Unexpected detached subtree found when ' +
-        'traversing DOM from node `%s`.',
-        nodeID
-      );
+      if (current == null) {
+        // The passed-in node has been detached from the container it was
+        // originally rendered into.
+        return null;
+      }
     } while (lastID !== reactRootID);
 
     if (current === containersByReactRootID[reactRootID]) {

src/renderers/dom/client/__tests__/ReactEventIndependence-test.js

@@ -0,0 +1,70 @@
+/**
+ * Copyright 2013-2015, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ *
+ * @emails react-core
+ */
+
+'use strict';
+
+var React;
+var ReactDOM;
+var ReactTestUtils;
+
+describe('ReactEventIndependence', function() {
+  beforeEach(function() {
+    require('mock-modules').dumpCache();
+
+    React = require('React');
+    ReactDOM = require('ReactDOM');
+    ReactTestUtils = require('ReactTestUtils');
+  });
+
+  it('does not crash with other react inside', function() {
+    var clicks = 0;
+    var div = ReactTestUtils.renderIntoDocument(
+      <div
+        onClick={() => clicks++}
+        dangerouslySetInnerHTML={{
+          __html: '<button data-reactid=".z">click me</div>',
+        }}
+      />
+    );
+    ReactTestUtils.SimulateNative.click(div.firstChild);
+    expect(clicks).toBe(1);
+  });
+
+  it('does not crash with other react outside', function() {
+    var clicks = 0;
+    var outer = document.createElement('div');
+    outer.setAttribute('data-reactid', '.z');
+    var inner = ReactDOM.render(
+      <button onClick={() => clicks++}>click me</button>,
+      outer
+    );
+    ReactTestUtils.SimulateNative.click(inner);
+    expect(clicks).toBe(1);
+  });
+
+  it('does not when event fired on unmounted tree', function() {
+    var clicks = 0;
+    var container = document.createElement('div');
+    var button = ReactDOM.render(
+      <button onClick={() => clicks++}>click me</button>,
+      container
+    );
+
+    // Now we unmount the component, as if caused by a non-React event handler
+    // for the same click we're about to simulate, like closing a layer:
+    ReactDOM.unmountComponentAtNode(container);
+    ReactTestUtils.SimulateNative.click(button);
+
+    // Since the tree is unmounted, we don't dispatch the click event.
+    expect(clicks).toBe(0);
+  });
+
+});