Move dart2js entrypoint detection into isPrimary.

sdk/lib/_internal/pub/test/build/reports_dart_parse_errors_test.dart

Index: sdk/lib/_internal/pub/test/build/reports_dart_parse_errors_test.dart
diff --git a/sdk/lib/_internal/pub/test/build/reports_dart_parse_errors_test.dart b/sdk/lib/_internal/pub/test/build/reports_dart_parse_errors_test.dart
index 1e5e1441f1e9a257005079b27348038637d4bdc0..bd0db6891fb0c043a1f5bcb8a8a5345f7abbac9a 100644
--- a/sdk/lib/_internal/pub/test/build/reports_dart_parse_errors_test.dart
+++ b/sdk/lib/_internal/pub/test/build/reports_dart_parse_errors_test.dart
@@ -2,7 +2,9 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+import 'package:path/path.dart' as p;
 import 'package:scheduled_test/scheduled_test.dart';
+import 'package:scheduled_test/scheduled_stream.dart';
 
 import '../../lib/src/exit_codes.dart' as exit_codes;
 import '../descriptor.dart' as d;
@@ -27,16 +29,25 @@ main() {
       ])
     ]).create();
 
-    schedulePub(args: ["build"],
-        // TODO(rnystrom): Figure out why dart2js errors aren't deterministic.
-        // Use a lookahead regexp to do two searches in one regexp.
-        // Checked all non-matching cases for bad performance.
-        error: new RegExp(
-            r"(?=(.|\n)*^Error in .*[/\\]file\.dart:)"
-            r"(.|\n)*^Error in .*[/\\]subfile\.dart:",
-            multiLine: true),
-        output: new RegExp(r"Building myapp\.\.\.*"),
-        exitCode: exit_codes.DATA);
+    var pub = startPub(args: ["build"]);
+    pub.stdout.expect(startsWith("Building myapp..."));
+
+    var consumeFile = consumeThrough(inOrder([
+      "[Error from Dart2JS]:",
+      startsWith(p.join("web", "file.dart") + ":")
+    ]));
+    var consumeSubfile = consumeThrough(inOrder([
+      "[Error from Dart2JS]:",
+      startsWith(p.join("web", "subdir", "subfile.dart") + ":")
+    ]));
+
+    // It's nondeterministic what order the dart2js transformers start running,
+    // so we allow the error messages to be emitted in either order.
+    pub.stderr.expect(either(
+        inOrder([consumeFile, consumeSubfile]),
+        inOrder([consumeSubfile, consumeFile])));
+
+    pub.shouldExit(exit_codes.DATA);
 
     // Doesn't output anything if an error occurred.
     d.dir(appPath, [