Add fallback support/test.

src/lib/annotations/annotations.html

@@ -273,6 +273,10 @@
     _replaceSlotWithContent: function(slot) {
       var content = slot.ownerDocument.createElement('content');
       var attrs = slot.attributes;
+      var childNodes = slot.childNodes;
+      while (slot.firstChild) {
+        content.appendChild(slot.firstChild);
+      }
       for (var i=0; i<attrs.length; i++) {
         var attr = attrs[i];
         content.setAttribute(attr.name, attr.value);

test/unit/polymer-dom-content.html

@@ -32,8 +32,8 @@
 <dom-module id="x-dist-slot">
   <template>
     x-dist
-    <div id="default"><slot id="defaultIP"></slot></div>
-    <div id="foo"><slot id="fooIP" name="foo"></slot></div>
+    <div id="default"><slot id="defaultIP"><div>fallback for default</div></slot></div>
+    <div id="foo"><slot id="fooIP" name="foo"><div>fallback for foo</div></slot></div>
   </template>
   <script>
   HTMLImports.whenReady(function() {
@@ -357,6 +357,10 @@
       assert.equal(dist.$.fooIP.getAttribute('select'), '[slot=\'foo\']');
       assert.equal(dist.$.defaultIP.localName, 'content');
       assert.equal(dist.$.defaultIP.getAttribute('select'), ':not([slot])');
+      if (usingShady) {
+        assert.equal(dist.$.foo.firstElementChild.textContent, 'fallback for foo');
+        assert.equal(dist.$.default.firstElementChild.textContent, 'fallback for default');
+      }
       // Distribute div
       var frag = document.createDocumentFragment();
       var foo1 = frag.appendChild(document.createElement('div'));
@@ -380,9 +384,9 @@
       Polymer.dom(dist).removeChild(default2);
       Polymer.dom.flush();
       if (usingShady) {
-        assert.equal(dist.$.foo.children[0], null);
+        assert.equal(dist.$.foo.children[0].textContent, 'fallback for foo');
         assert.equal(dist.$.foo.children[1], null);
-        assert.equal(dist.$.default.children[0], null);
+        assert.equal(dist.$.default.children[0].textContent, 'fallback for default');
         assert.equal(dist.$.default.children[1], null);
       }
       document.body.removeChild(dist);