Don't blow up on missing _store in element validation

Seems better to fail gracefully, especially now that we support inlining. If people do this by accident we can figure out how to add a helpful warning instead.

Fixes #3285.

src/isomorphic/classic/element/ReactElementValidator.js

@@ -57,7 +57,7 @@ var loggedTypeFailures = {};
  * @param {*} parentType element's parent's type.
  */
 function validateExplicitKey(element, parentType) {
-  if (element._store.validated || element.key != null) {
+  if (!element._store || element._store.validated || element.key != null) {
     return;
   }
   element._store.validated = true;

src/isomorphic/classic/element/__tests__/ReactElementValidator-test.js

@@ -467,4 +467,20 @@ describe('ReactElementValidator', function() {
     }
   });
 
+  it('does not blow up with inlined children', function() {
+    // We don't suggest this since it silences all sorts of warnings, but we
+    // shouldn't blow up either.
+
+    var child = {
+      $$typeof: (<div />).$$typeof,
+      type: 'span',
+      key: null,
+      ref: null,
+      props: {},
+      _owner: null,
+    };
+
+    void <div>{[child]}</div>;
+  });
+
 });