Improves how to initialize polymer apps and fixes polymer build and linter to

pkg/polymer/lib/src/build/polyfill_injector.dart

Index: pkg/polymer/lib/src/build/polyfill_injector.dart
diff --git a/pkg/polymer/lib/src/build/polyfill_injector.dart b/pkg/polymer/lib/src/build/polyfill_injector.dart
index 3bf7e7a671c28584c5099d5f711768e1df24eede..acc0d7185c9b80267f7f90dbeb760702bb20d085 100644
--- a/pkg/polymer/lib/src/build/polyfill_injector.dart
+++ b/pkg/polymer/lib/src/build/polyfill_injector.dart
@@ -36,6 +36,7 @@ class PolyfillInjector extends Transformer with PolymerTransformer {
       bool jsInteropFound = false;
       bool customElementFound = false;
       bool dartScriptTags = false;
+      bool dartLoaderTagFound = false;
 
       for (var tag in document.queryAll('script')) {
         var src = tag.attributes['src'];
@@ -47,6 +48,8 @@ class PolyfillInjector extends Transformer with PolymerTransformer {
             shadowDomFound = true;
           } else if (_customElementJS.hasMatch(last)) {
             customElementFound = true;
+          } else if (last == 'dart.js') {
+            dartLoaderTagFound = true;
           }
         }
 
@@ -62,7 +65,7 @@ class PolyfillInjector extends Transformer with PolymerTransformer {
       }
 
       _addScript(urlSegment) {
-        document.body.nodes.insert(0, parseFragment(
+        document.head.nodes.insert(0, parseFragment(
               '<script src="packages/$urlSegment"></script>\n'));
       }
 
@@ -72,10 +75,15 @@ class PolyfillInjector extends Transformer with PolymerTransformer {
         _addScript('custom_element/custom-elements.debug.js');
       }
 
-      // This polyfill needs to be the first one on the body
+      // This polyfill needs to be the first one on the head
       // TODO(jmesserly): this is .debug to workaround issue 13046.
       if (!shadowDomFound) _addScript('shadow_dom/shadow_dom.debug.js');
 
+      if (!dartLoaderTagFound) {
+        document.body.nodes.add(parseFragment(
+              '<script src="packages/browser/dart.js"></script>'));
+      }
+
       transform.addOutput(
           new Asset.fromString(transform.primaryInput.id, document.outerHtml));
     });