Refactoring two pieces of polymer:

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 f3dc5e86e27becce5afdfd415909524c945ceffa..54533c974c9b31dcaea5295851044d7dffca4e8f 100644
--- a/pkg/polymer/lib/src/loader.dart
+++ b/pkg/polymer/lib/src/loader.dart
@@ -12,7 +12,13 @@ class CustomTag {
 
 /// Metadata used to label static or top-level methods that are called
 /// automatically when loading the library of a custom element.
-const initMethod = const _InitMethodAnnotation();
+const initMethod = const InitMethodAnnotation();
+
+/// Implementation behind [initMethod]. Only exposed for internal implementation
+/// details
+class InitMethodAnnotation {
+  const InitMethodAnnotation();
+}
 
 /// Initializes a polymer application as follows:
 ///   * set up up polling for observable changes
@@ -22,33 +28,19 @@ const initMethod = const _InitMethodAnnotation();
 ///   register custom elements declared there (labeled with [CustomTag]) and
 ///   invoke the initialization method on it (top-level functions annotated with
 ///   [initMethod]).
-Zone initPolymer() {
-  // We use this pattern, and not the inline lazy initialization pattern, so we
-  // can help dart2js detect that _discoverInitializers can be tree-shaken for
-  // deployment (and hence all uses of dart:mirrors from this loading logic).
-  // TODO(sigmund): fix polymer's transformers so they can replace initPolymer
-  // by initPolymerOptimized.
-  if (_initializers == null) _initializers = _discoverInitializers();
-
+Zone initPolymer() => loader.deployMode
   // In deployment mode, we rely on change notifiers instead of dirty checking.
-  if (!_deployMode) {
-    return dirtyCheckZone()..run(initPolymerOptimized);
-  }
-
-  return initPolymerOptimized();
-}
+    ? _initPolymerOptimized() : (dirtyCheckZone()..run(_initPolymerOptimized));
 
 /// Same as [initPolymer], but runs the version that is optimized for deployment
 /// to the internet. The biggest difference is it omits the [Zone] that
 /// automatically invokes [Observable.dirtyCheck], and the list of initializers
 /// must be supplied instead of being dynamically searched for at runtime using
 /// mirrors.
-Zone initPolymerOptimized() {
-  // TODO(sigmund): refactor this so we can replace it by codegen.
-  smoke.useMirrors();
+Zone _initPolymerOptimized() {
   _hookJsPolymer();
 
-  for (var initializer in _initializers) {
+  for (var initializer in loader.initializers) {
     initializer();
   }
 
@@ -60,200 +52,8 @@ Zone initPolymerOptimized() {
 /// at runtime. Additionally, after this method is called [initPolymer] omits
 /// the [Zone] that automatically invokes [Observable.dirtyCheck].
 void configureForDeployment(List<Function> initializers) {
-  _initializers = initializers;
-  _deployMode = true;
-}
-
-/// List of initializers that by default will be executed when calling
-/// initPolymer. If null, initPolymer will compute the list of initializers by
-/// crawling HTML imports, searchfing for script tags, and including an
-/// initializer for each type tagged with a [CustomTag] annotation and for each
-/// top-level method annotated with [initMethod]. The value of this field is
-/// assigned programatically by the code generated from the polymer deploy
-/// scripts.
-List<Function> _initializers;
-
-/// True if we're in deployment mode.
-bool _deployMode = false;
-
-List<Function> _discoverInitializers() {
-  var initializers = [];
-  var librariesToLoad = _discoverScripts(document, window.location.href);
-  for (var lib in librariesToLoad) {
-    try {
-      _loadLibrary(lib, initializers);
-    } catch (e, s) {
-      // Deliver errors async, so if a single library fails it doesn't prevent
-      // other things from loading.
-      new Completer().completeError(e, s);
-    }
-  }
-  return initializers;
-}
-
-/// Walks the HTML import structure to discover all script tags that are
-/// implicitly loaded. This code is only used in Dartium and should only be
-/// called after all HTML imports are resolved. Polymer ensures this by asking
-/// users to put their Dart script tags after all HTML imports (this is checked
-/// by the linter, and Dartium will otherwise show an error message).
-List<String> _discoverScripts(Document doc, String baseUri,
-    [Set<Document> seen, List<String> scripts]) {
-  if (seen == null) seen = new Set<Document>();
-  if (scripts == null) scripts = <String>[];
-  if (doc == null) {
-    print('warning: $baseUri not found.');
-    return scripts;
-  }
-  if (seen.contains(doc)) return scripts;
-  seen.add(doc);
-
-  bool scriptSeen = false;
-  for (var node in doc.querySelectorAll('script,link[rel="import"]')) {
-    if (node is LinkElement) {
-      _discoverScripts(node.import, node.href, seen, scripts);
-    } else if (node is ScriptElement && node.type == 'application/dart') {
-      if (!scriptSeen) {
-        var url = node.src;
-        scripts.add(url == '' ? baseUri : url);
-        scriptSeen = true;
-      } else {
-        print('warning: more than one Dart script tag in $baseUri. Dartium '
-            'currently only allows a single Dart script tag per document.');
-      }
-    }
-  }
-  return scripts;
-}
-
-/// All libraries in the current isolate.
-final _libs = currentMirrorSystem().libraries;
-
-// TODO(sigmund): explore other (cheaper) ways to resolve URIs relative to the
-// root library (see dartbug.com/12612)
-final _rootUri = currentMirrorSystem().isolate.rootLibrary.uri;
-
-final Logger _loaderLog = new Logger('polymer.loader');
-
-bool _isHttpStylePackageUrl(Uri uri) {
-  var uriPath = uri.path;
-  return uri.scheme == _rootUri.scheme &&
-      // Don't process cross-domain uris.
-      uri.authority == _rootUri.authority &&
-      uriPath.endsWith('.dart') &&
-      (uriPath.contains('/packages/') || uriPath.startsWith('packages/'));
-}
-
-/// Reads the library at [uriString] (which can be an absolute URI or a relative
-/// URI from the root library), and:
-///
-///   * If present, invokes any top-level and static functions marked
-///     with the [initMethod] annotation (in the order they appear).
-///
-///   * Registers any [PolymerElement] that is marked with the [CustomTag]
-///     annotation.
-void _loadLibrary(String uriString, List<Function> initializers) {
-  var uri = _rootUri.resolve(uriString);
-  var lib = _libs[uri];
-  if (_isHttpStylePackageUrl(uri)) {
-    // Use package: urls if available. This rule here is more permissive than
-    // how we translate urls in polymer-build, but we expect Dartium to limit
-    // the cases where there are differences. The polymer-build issues an error
-    // when using packages/ inside lib without properly stepping out all the way
-    // to the packages folder. If users don't create symlinks in the source
-    // tree, then Dartium will also complain because it won't find the file seen
-    // in an HTML import.
-    var packagePath = uri.path.substring(
-        uri.path.lastIndexOf('packages/') + 'packages/'.length);
-    var canonicalLib = _libs[Uri.parse('package:$packagePath')];
-    if (canonicalLib != null) {
-      lib = canonicalLib;
-    }
-  }
-
-  if (lib == null) {
-    _loaderLog.info('$uri library not found');
-    return;
-  }
-
-  // Search top-level functions marked with @initMethod
-  for (var f in lib.declarations.values.where((d) => d is MethodMirror)) {
-    _addInitMethod(lib, f, initializers);
-  }
-
-
-  // Dart note: we don't get back @CustomTags in a reliable order from mirrors,
-  // at least on Dart VM. So we need to sort them so base classes are registered
-  // first, which ensures that document.register will work correctly for a
-  // set of types within in the same library.
-  var customTags = new LinkedHashMap<Type, Function>();
-  for (var c in lib.declarations.values.where((d) => d is ClassMirror)) {
-    _loadCustomTags(lib, c, customTags);
-    // TODO(sigmund): check also static methods marked with @initMethod.
-    // This is blocked on two bugs:
-    //  - dartbug.com/12133 (static methods are incorrectly listed as top-level
-    //    in dart2js, so they end up being called twice)
-    //  - dartbug.com/12134 (sometimes "method.metadata" throws an exception,
-    //    we could wrap and hide those exceptions, but it's not ideal).
-  }
-
-  initializers.addAll(customTags.values);
-}
-
-void _loadCustomTags(LibraryMirror lib, ClassMirror cls,
-    LinkedHashMap registerFns) {
-  if (cls == null || cls.reflectedType == HtmlElement) return;
-
-  // Register superclass first.
-  _loadCustomTags(lib, cls.superclass, registerFns);
-
-  if (cls.owner != lib) {
-    // Don't register classes from different libraries.
-    // TODO(jmesserly): @CustomTag does not currently respect re-export, because
-    // LibraryMirror.declarations doesn't include these.
-    return;
-  }
-
-  var meta = _getCustomTagMetadata(cls);
-  if (meta == null) return;
-
-  registerFns.putIfAbsent(cls.reflectedType, () =>
-      () => Polymer.register(meta.tagName, cls.reflectedType));
-}
-
-/// Search for @CustomTag on a classemirror
-CustomTag _getCustomTagMetadata(ClassMirror c) {
-  for (var m in c.metadata) {
-    var meta = m.reflectee;
-    if (meta is CustomTag) return meta;
-  }
-  return null;
-}
-
-void _addInitMethod(ObjectMirror obj, MethodMirror method,
-    List<Function> initializers) {
-  var annotationFound = false;
-  for (var meta in method.metadata) {
-    if (identical(meta.reflectee, initMethod)) {
-      annotationFound = true;
-      break;
-    }
-  }
-  if (!annotationFound) return;
-  if (!method.isStatic) {
-    print("warning: methods marked with @initMethod should be static,"
-        " ${method.simpleName} is not.");
-    return;
-  }
-  if (!method.parameters.where((p) => !p.isOptional).isEmpty) {
-    print("warning: methods marked with @initMethod should take no "
-        "arguments, ${method.simpleName} expects some.");
-    return;
-  }
-  initializers.add(() => obj.invoke(method.simpleName, const []));
-}
-
-class _InitMethodAnnotation {
-  const _InitMethodAnnotation();
+  loader.initializers = initializers;
+  loader.deployMode = true;
 }
 
 /// To ensure Dart can interoperate with polymer-element registered by