refactor(transformer): precompile stylesheets

Part of #3605

modules_dart/transform/lib/src/transform/stylesheet_compiler/processor.dart

@@ -0,0 +1,37 @@
+library angular2.transform.stylesheet_compiler.processor;
+
+import 'dart:async';
+
+import 'package:angular2/src/transform/common/asset_reader.dart';
+import 'package:angular2/src/transform/common/code/source_module.dart';
+import 'package:angular2/src/transform/common/names.dart';
+import 'package:angular2/src/transform/common/ng_compiler.dart';
+import 'package:angular2/src/compiler/source_module.dart';
+
+import 'package:barback/barback.dart';
+
+AssetId shimmedStylesheetAssetId(AssetId cssAssetId) => new AssetId(
+    cssAssetId.package, toShimmedStylesheetExtension(cssAssetId.path));
+
+AssetId nonShimmedStylesheetAssetId(AssetId cssAssetId) => new AssetId(
+    cssAssetId.package, toNonShimmedStylesheetExtension(cssAssetId.path));
+
+Future<Iterable<Asset>> processStylesheet(
+    AssetReader reader, AssetId stylesheetId) async {
+  final stylesheetUrl = '${stylesheetId.package}|${stylesheetId.path}';
+  final templateCompiler = createTemplateCompiler(reader);
+  final cssText = await reader.readAsString(stylesheetId);
+  final sourceModules =
+      templateCompiler.compileStylesheetCodeGen(stylesheetUrl, cssText);
+
+  var libraryIdx = 0;
+  return sourceModules.map((SourceModule module) => new Asset.fromString(
+      new AssetId.parse('${module.moduleUrl}'),
+      writeSourceModule(module,
+          libraryName: '${_getLibBase(module.moduleUrl)}${libraryIdx++}')));
+}
+
+final _unsafeCharsPattern = new RegExp(r'[^a-zA-Z0-9_]');
+String _getLibBase(String libraryName) {
+  return libraryName.replaceAll('/', '.').replaceAll(_unsafeCharsPattern, '_');
+}

modules_dart/transform/lib/src/transform/stylesheet_compiler/transformer.dart

@@ -0,0 +1,40 @@
+library angular2.transform.stylesheet_compiler.transformer;
+
+import 'dart:async';
+
+import 'package:angular2/src/core/dom/html_adapter.dart';
+import 'package:angular2/src/transform/common/asset_reader.dart';
+import 'package:angular2/src/transform/common/logging.dart' as log;
+import 'package:angular2/src/transform/common/names.dart';
+
+import 'package:barback/barback.dart';
+
+import 'processor.dart';
+
+/// Pre-compiles CSS stylesheet files to Dart code for Angular 2.
+class StylesheetCompiler extends Transformer implements DeclaringTransformer {
+  StylesheetCompiler();
+
+  @override
+  bool isPrimary(AssetId id) {
+    return id.path.endsWith(CSS_EXTENSION);
+  }
+
+  @override
+  declareOutputs(DeclaringTransform transform) {
+    transform.declareOutput(nonShimmedStylesheetAssetId(transform.primaryId));
+    transform.declareOutput(shimmedStylesheetAssetId(transform.primaryId));
+  }
+
+  @override
+  Future apply(Transform transform) async {
+    await log.initZoned(transform, () async {
+      Html5LibDomAdapter.makeCurrent();
+      var reader = new AssetReader.fromTransform(transform);
+      var outputs = await processStylesheet(reader, transform.primaryInput.id);
+      outputs.forEach((Asset compiledStylesheet) {
+        transform.addOutput(compiledStylesheet);
+      });
+    });
+  }
+}