Move js library back into compiler directory.

tools/testing/dart/compiler_configuration.dart

Index: tools/testing/dart/compiler_configuration.dart
diff --git a/tools/testing/dart/compiler_configuration.dart b/tools/testing/dart/compiler_configuration.dart
index 3407c67f1eb7c5a9944e7b5cd6d7a760887eb68e..20ab1c77163774da2d5fa9021a06c82e0e88c58b 100644
--- a/tools/testing/dart/compiler_configuration.dart
+++ b/tools/testing/dart/compiler_configuration.dart
@@ -275,7 +275,7 @@ class Dart2jsCompilerConfiguration extends Dart2xCompilerConfiguration {
     Uri sdk = useSdk ?
         nativeDirectoryToUri(buildDir).resolve('dart-sdk/') :
         nativeDirectoryToUri(TestUtils.dartDir.toNativePath()).resolve('sdk/');
-    Uri preambleDir = sdk.resolve('lib/_internal/lib/preambles/');
+    Uri preambleDir = sdk.resolve('lib/_internal/compiler/js_lib/preambles/');
     return runtimeConfiguration.dart2jsPreambles(preambleDir)
         ..add(artifact.filename);
   }