Use failedAt in more places

pkg/compiler/lib/src/compiler.dart

 // Copyright (c) 2012, 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 file.
 
 library dart2js.compiler_base;
 
 import 'dart:async' show Future;
 
 import '../compiler_new.dart' as api;
 import 'backend_strategy.dart';
@@ skipping 842 matching lines @@
     }
     registerCompileTimeError(currentElement, message);
   }
 
   /**
    * Reads the script specified by the [readableUri].
    *
    * See [LibraryLoader] for terminology on URIs.
    */
   Future<Script> readScript(Uri readableUri, [Spannable node]) {
-    throw new SpannableAssertionFailure(
-        node, 'Compiler.readScript not implemented.');
+    throw failedAt(node, 'Compiler.readScript not implemented.');
   }
 
   Future<Binary> readBinary(Uri readableUri, [Spannable node]) {
-    throw new SpannableAssertionFailure(
-        node, 'Compiler.readBinary not implemented.');
+    throw failedAt(node, 'Compiler.readBinary not implemented.');
   }
 
   Element lookupElementIn(ScopeContainerElement container, String name) {
     Element element = container.localLookup(name);
     if (element == null) {
       throw 'Could not find $name in $container';
     }
     return element;
   }
 
@@ skipping 720 matching lines @@
   _ElementScanner(this.scanner);
   void scanLibrary(LibraryElement library) => scanner.scanLibrary(library);
   void scanUnit(CompilationUnitElement unit) => scanner.scan(unit);
 }
 
 class _EmptyEnvironment implements Environment {
   const _EmptyEnvironment();
 
   String valueOf(String key) => null;
 }