Apply several phases only to entrypoint files (which currently are identified as

pkg/polymer/lib/src/transform/common.dart

Index: pkg/polymer/lib/src/transform/common.dart
diff --git a/pkg/polymer/lib/src/transform/common.dart b/pkg/polymer/lib/src/transform/common.dart
index f20d836f7f71055d1094fdad196cd286f013d567..72abba952de15d53d84d80cb4c192f9e41425a34 100644
--- a/pkg/polymer/lib/src/transform/common.dart
+++ b/pkg/polymer/lib/src/transform/common.dart
@@ -72,3 +72,9 @@ AssetId resolve(AssetId source, String url, TransformLogger logger, Span span) {
   }
   return new AssetId(package, targetPath);
 }
+
+/** Whether an asset with [id] is considered a primary entry point HTML file. */
+Future<bool> isPrimaryHtml(AssetId id) =>
+    new Future.value(id.extension == '.html' &&
+        // Note: [id.path] is a relative path from the root of a package.
+        (id.path.startsWith('web/') || id.path.startsWith('test/')));