Practically remove boot.js, adds the initialization from the Dart side of

pkg/polymer/test/build/script_compactor_test.dart

Index: pkg/polymer/test/build/script_compactor_test.dart
diff --git a/pkg/polymer/test/build/script_compactor_test.dart b/pkg/polymer/test/build/script_compactor_test.dart
index e0977bebeb9a08d53c520481d6b2f645d758504b..74eab9e0b5b21eacc2b0a08214e1989b1d15d2fd 100644
--- a/pkg/polymer/test/build/script_compactor_test.dart
+++ b/pkg/polymer/test/build/script_compactor_test.dart
@@ -49,7 +49,7 @@ void main() {
           void main() {
             initPolymer([
                 'a.dart',
-              ], currentMirrorSystem().isolate.rootLibrary.uri.toString());
+              ]);
           }
           '''.replaceAll('\n          ', '\n'),
     });
@@ -84,7 +84,7 @@ void main() {
                 'b.dart',
                 'c.dart',
                 'd.dart',
-              ], currentMirrorSystem().isolate.rootLibrary.uri.toString());
+              ]);
           }
           '''.replaceAll('\n          ', '\n'),
     });