Change IllegalArgumentException to ArgumentError.

tests/compiler/dart2js/mock_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('mock_compiler');
 
 #import("dart:uri");
 
 #import("../../../lib/compiler/implementation/elements/elements.dart");
 #import("../../../lib/compiler/implementation/leg.dart");
@@ skipping 162 matching lines @@
 
   void importCoreLibrary(LibraryElement library) {
     scanner.importLibrary(library, coreLibrary, null);
   }
 
   // The mock library doesn't need any patches.
   Uri resolvePatchUri(String dartLibraryName) => null;
 
   Script readScript(Uri uri, [ScriptTag node]) {
     SourceFile sourceFile = sourceFiles[uri.toString()];
-    if (sourceFile === null) throw new IllegalArgumentException(uri);
+    if (sourceFile === null) throw new ArgumentError(uri);
     return new Script(uri, sourceFile);
   }
 }
 
 void compareWarningKinds(String text, expectedWarnings, foundWarnings) {
   var fail = (message) => Expect.fail('$text: $message');
   Iterator<MessageKind> expected = expectedWarnings.iterator();
   Iterator<WarningMessage> found = foundWarnings.iterator();
   while (expected.hasNext() && found.hasNext()) {
     Expect.equals(expected.next(), found.next().message.kind);
@@ skipping 20 matching lines @@
     });
   }
 }
 
 LibraryElement mockLibrary(Compiler compiler, String source) {
   Uri uri = new Uri.fromComponents(scheme: "source");
   var library = new LibraryElement(new Script(uri, new MockFile(source)));
   importLibrary(library, compiler.coreLibrary, compiler);
   return library;
 }