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

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

Index: editor/tools/plugins/com.google.dart.engine/src/com/google/dart/engine/ast/ClassDeclaration.java
diff --git a/editor/tools/plugins/com.google.dart.engine/src/com/google/dart/engine/ast/ClassDeclaration.java b/editor/tools/plugins/com.google.dart.engine/src/com/google/dart/engine/ast/ClassDeclaration.java
index b954736a02bc8007f37723f579d06e000335069c..38ecc21ad2159382fc95f3dac2852e521b17b778 100644
--- a/editor/tools/plugins/com.google.dart.engine/src/com/google/dart/engine/ast/ClassDeclaration.java
+++ b/editor/tools/plugins/com.google.dart.engine/src/com/google/dart/engine/ast/ClassDeclaration.java
@@ -304,6 +304,15 @@ public class ClassDeclaration extends CompilationUnitMember {
   }
 
   /**
+   * 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 'abstract' keyword to the given keyword.
    * 
    * @param abstractKeyword the 'abstract' keyword