Add regression tests.

lib/custom_compiler.dart

 // Copyright (c) 2016, the Dart project authors. Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
 library rasta.custom_compiler;
 
 import 'package:compiler/src/apiimpl.dart' show
     CompilerImpl;
 
 import 'package:compiler/compiler_new.dart' show
@@ skipping 112 matching lines @@
   void recoverFromCrash() {
     if (reporter is CompilerDiagnosticReporter) {
       CompilerDiagnosticReporter reporter = this.reporter;
       reporter.hasCrashed = false;
     }
     if (handler is FormattingDiagnosticHandler) {
       FormattingDiagnosticHandler handler = this.handler;
       handler.isAborting = false;
     }
     enqueuer.resolution.deferredTaskQueue.clear();
+    (libraryLoader as dynamic).currentHandler = null;
   }
 
   bool get isInternalStateConsistent {
     if (reporter is CompilerDiagnosticReporter) {
       CompilerDiagnosticReporter reporter = this.reporter;
       if (reporter.hasCrashed) {
         print("Reporter hasCrashed");
         return false;
       }
     }
     if (handler is FormattingDiagnosticHandler) {
       FormattingDiagnosticHandler handler = this.handler;
       if (handler.isAborting) {
         print("Reporter isAborting");
         return false;
       }
     }
     if (enqueuer.resolution.deferredTaskQueue.isNotEmpty) {
       print("Resolution deferredTaskQueue isn't empty");
       return false;
     }
+    if ((libraryLoader as dynamic).currentHandler != null) {
+      print("compiler.libraryLoader.currentHandler isn't null");
+      return false;
+    }
     return true;
   }
 }