feat(dart/transform): Allow multiple transformer entry points

- Allow the user to specify multiple entry points to an app.
- Allow the Angular 2 transformer to run without explicit entry points to
generate necessary setters & getters on built-in directives like `For`
and `If`.

Closes #1246

modules/angular2/src/transform/common/options.dart

@@ -1,35 +1,29 @@
 library angular2.transform.common.options;
 
-const ENTRY_POINT_PARAM = 'entry_point';
-const REFLECTION_ENTRY_POINT_PARAM = 'reflection_entry_point';
+const ENTRY_POINT_PARAM = 'entry_points';
+const REFLECTION_ENTRY_POINT_PARAM = 'reflection_entry_points';
 
 /// Provides information necessary to transform an Angular2 app.
 class TransformerOptions {
-  /// The path to the file where the application's call to [bootstrap] is.
-  // TODO(kegluneq): Allow multiple entry points.
-  final String entryPoint;
+  /// The path to the files where the application's calls to `bootstrap` are.
+  final List<String> entryPoints;
 
-  /// The reflection entry point, that is, the path to the file where the
-  /// application's [ReflectionCapabilities] are set.
-  final String reflectionEntryPoint;
+  /// The paths to the files where the application's [ReflectionCapabilities]
+  /// are set.
+  final List<String> reflectionEntryPoints;
 
   /// The `BarbackMode#name` we are running in.
   final String modeName;
 
   TransformerOptions._internal(
-      this.entryPoint, this.reflectionEntryPoint, this.modeName);
+      this.entryPoints, this.reflectionEntryPoints, this.modeName);
 
-  factory TransformerOptions(String entryPoint,
-      {String reflectionEntryPoint, String modeName: 'release'}) {
-    if (entryPoint == null) {
-      throw new ArgumentError.notNull(ENTRY_POINT_PARAM);
-    } else if (entryPoint.isEmpty) {
-      throw new ArgumentError.value(entryPoint, 'entryPoint');
-    }
-    if (reflectionEntryPoint == null || entryPoint.isEmpty) {
-      reflectionEntryPoint = entryPoint;
+  factory TransformerOptions(List<String> entryPoints,
+      {List<String> reflectionEntryPoints, String modeName: 'release'}) {
+    if (reflectionEntryPoints == null || reflectionEntryPoints.isEmpty) {
+      reflectionEntryPoints = entryPoints;
     }
     return new TransformerOptions._internal(
-        entryPoint, reflectionEntryPoint, modeName);
+        entryPoints, reflectionEntryPoints, modeName);
   }
 }

modules/angular2/src/transform/common/options_reader.dart

@@ -0,0 +1,36 @@
+library angular2.transform.common.options;
+
+import 'package:barback/barback.dart';
+import 'options.dart';
+
+TransformerOptions parseBarbackSettings(BarbackSettings settings) {
+  var config = settings.configuration;
+  var entryPoints = _readFileList(config, ENTRY_POINT_PARAM);
+  var reflectionEntryPoints =
+      _readFileList(config, REFLECTION_ENTRY_POINT_PARAM);
+  return new TransformerOptions(entryPoints,
+      reflectionEntryPoints: reflectionEntryPoints,
+      modeName: settings.mode.name);
+}
+
+/// Cribbed from the polymer project.
+/// [https://github.com/dart-lang/polymer-dart]
+List<String> _readFileList(Map config, String paramName) {
+  var value = config[paramName];
+  if (value == null) return null;
+  var files = [];
+  bool error = false;
+  if (value is List) {
+    files = value;
+    error = value.any((e) => e is! String);
+  } else if (value is String) {
+    files = [value];
+    error = false;
+  } else {
+    error = true;
+  }
+  if (error) {
+    print('Invalid value for "$paramName" in the Angular 2 transformer.');
+  }
+  return files;
+}