Add ClassDeclaration/ClassTypeAlias.isAbstract() and use them.

editor/tools/plugins/com.google.dart.engine/src/com/google/dart/engine/ast/ClassTypeAlias.java

 /*
  * Copyright 2012, the Dart project authors.
  * 
  * Licensed under the Eclipse Public License v1.0 (the "License"); you may not use this file except
  * in compliance with the License. You may obtain a copy of the License at
  * 
  * http://www.eclipse.org/legal/epl-v10.html
  * 
  * Unless required by applicable law or agreed to in writing, software distributed under the License
  * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
@@ skipping 155 matching lines @@
   /**
    * Return the with clause for this class.
    * 
    * @return the with clause for this class
    */
   public WithClause getWithClause() {
     return withClause;
   }
 
   /**
+   * Return {@code true} if this class is declared to be an abstract class.
+   * 
+   * @return {@code true} if this class is declared to be an abstract class
+   */
+  public boolean isAbstract() {
+    return abstractKeyword != null;
+  }
+
+  /**
    * Set the token for the 'abstract' keyword to the given token.
    * 
    * @param abstractKeyword the token for the 'abstract' keyword
    */
   public void setAbstractKeyword(Token abstractKeyword) {
     this.abstractKeyword = abstractKeyword;
   }
 
   /**
    * Set the token for the '=' separating the name from the definition to the given token.
@@ skipping 52 matching lines @@
   @Override
   public void visitChildren(AstVisitor<?> visitor) {
     super.visitChildren(visitor);
     safelyVisitChild(name, visitor);
     safelyVisitChild(typeParameters, visitor);
     safelyVisitChild(superclass, visitor);
     safelyVisitChild(withClause, visitor);
     safelyVisitChild(implementsClause, visitor);
   }
 }