Call bindFinished during template production and mark stagingDocument…

…. This will allow custom elements which wish to delay construction work if bindings are coming to detect that case and to know when binding is finished.

R=arv
BUG=

Review URL: https://codereview.appspot.com/88570043

src/TemplateBinding.js

@@ -264,7 +264,7 @@
       var owner = template.ownerDocument;
       if (!owner.stagingDocument_) {
         owner.stagingDocument_ = owner.implementation.createHTMLDocument('');
-
+        owner.stagingDocument_.isStagingDocument = true;
         // TODO(rafaelw): Remove when fix for
         // https://codereview.chromium.org/164803002/
         // makes it to Chrome release.
@@ -794,6 +794,7 @@
         instanceBindings.push(binding);
     }
 
+    node.bindFinished();
     if (!bindings.isTemplate)
       return;