Remove corelib/corelib_strong and migrate last two remaining tests.

pkg/dev_compiler/test/codegen_test.dart

Index: pkg/dev_compiler/test/codegen_test.dart
diff --git a/pkg/dev_compiler/test/codegen_test.dart b/pkg/dev_compiler/test/codegen_test.dart
index 99c9f08b737e70dcfd0f4ed3b5f6a9ace0b4f579..471038289c68fac53f8959c39afef5ee1cc3daf4 100644
--- a/pkg/dev_compiler/test/codegen_test.dart
+++ b/pkg/dev_compiler/test/codegen_test.dart
@@ -87,7 +87,7 @@ main(List<String> arguments) {
   var sharedCompiler = new ModuleCompiler(new AnalyzerOptions.basic(
       dartSdkSummaryPath: sdkSummaryFile, summaryPaths: summaryPaths));
 
-  var testDirs = ['language', 'corelib', 'lib'];
+  var testDirs = ['language', 'corelib_2', 'lib'];
 
   // Copy all of the test files and expanded multitest files to
   // gen/codegen_tests. We'll compile from there.