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

pkg/polymer/lib/src/loader.dart

Index: pkg/polymer/lib/src/loader.dart
diff --git a/pkg/polymer/lib/src/loader.dart b/pkg/polymer/lib/src/loader.dart
index c2e2f55a290e5f629eb0828f2f56f7ca7619a505..edfa5591dadd87a0325f08b244ac4b1c4dad91d7 100644
--- a/pkg/polymer/lib/src/loader.dart
+++ b/pkg/polymer/lib/src/loader.dart
@@ -32,7 +32,7 @@ const initMethod = const _InitMethodAnnotation();
  * The urls in [libraries] can be absolute or relative to
  * `currentMirrorSystem().isolate.rootLibrary.uri`.
  */
-void initPolymer([List<String> libraries]) {
+void initPolymer() {
   runMicrotask(() {
     // DOM events don't yet go through microtasks, so we catch those here.
     new Timer.periodic(new Duration(milliseconds: 125),
@@ -46,15 +46,15 @@ void initPolymer([List<String> libraries]) {
 
     // Note: we synchronously load all libraries because the script invoking
     // this is run after all HTML imports are resolved.
-    if (libraries == null) {
-      libraries = _discoverScripts(document, window.location.href);
-    }
-    _loadLibraries(libraries);
+    _loadLibraries();
   });
 }
 
-void _loadLibraries(libraries) {
-  for (var lib in libraries) {
+List<String> librariesToLoad =
+    _discoverScripts(document, window.location.href);
+
+void _loadLibraries() {
+  for (var lib in librariesToLoad) {
     _loadLibrary(lib);
   }
   Polymer._ready.complete();