Fix most warnings and other minor cleanups.

lib/compiler/implementation/scanner/scanner_task.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.
 
 class ScannerTask extends CompilerTask {
   ScannerTask(Compiler compiler) : super(compiler);
   String get name() => 'Scanner';
 
   void scan(CompilationUnitElement compilationUnit) {
     measure(() {
@@ skipping 39 matching lines @@
         imports.addLast(tag);
       } else if (tag.isLibrary()) {
         tagState = checkTag(TagState.LIBRARY, tag);
         if (library.libraryTag !== null) {
           compiler.cancel("duplicated library declaration", node: tag);
         } else {
           library.libraryTag = tag;
         }
       } else if (tag.isSource()) {
         tagState = checkTag(TagState.SOURCE, tag);
-        Script script = compiler.readScript(resolved, argument);
+        Script script = compiler.readScript(resolved, tag);
         CompilationUnitElement unit =
             new CompilationUnitElement(script, library);
         compiler.withCurrentElement(unit, () => scan(unit));
       } else if (tag.isResource()) {
         tagState = checkTag(TagState.RESOURCE, tag);
         compiler.reportWarning(tag, 'ignoring resource tag');
       } else {
         compiler.cancel("illegal script tag: ${tag.tag}", node: tag);
       }
     }
@@ skipping 129 matching lines @@
   static final int RESOURCE = 4;
 
   /** Next state. */
   static final List<int> NEXT =
       const <int>[NO_TAG_SEEN,
                   IMPORT, // Only one library tag is allowed.
                   IMPORT,
                   SOURCE,
                   RESOURCE];
 }