Move all flags to CompilerOptions (first step to stop passing the compiler to

pkg/compiler/lib/src/typechecker.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.typechecker;
 
 import 'common.dart';
 import 'common/names.dart' show
     Identifiers;
 import 'common/resolution.dart' show
@@ skipping 540 matching lines @@
   }
 
   /**
    * Check if a value of type [from] can be assigned to a variable, parameter or
    * return value of type [to].  If `isConst == true`, an error is emitted in
    * checked mode, otherwise a warning is issued.
    */
   bool checkAssignable(Spannable spannable, DartType from, DartType to,
                        {bool isConst: false}) {
     if (!types.isAssignable(from, to)) {
-      if (compiler.enableTypeAssertions && isConst) {
+      if (compiler.options.enableTypeAssertions && isConst) {
         reporter.reportErrorMessage(
             spannable,
             MessageKind.NOT_ASSIGNABLE,
             {'fromType': from, 'toType': to});
       } else {
         reporter.reportWarningMessage(
             spannable,
             MessageKind.NOT_ASSIGNABLE,
             {'fromType': from, 'toType': to});
       }
@@ skipping 1432 matching lines @@
 
   visitTypedef(Typedef node) {
     // Do not typecheck [Typedef] nodes.
   }
 
   visitNode(Node node) {
     reporter.internalError(node,
         'Unexpected node ${node.getObjectDescription()} in the type checker.');
   }
 }