Remove unnecessary casts and general code clean-up

pkg/analyzer/lib/src/generated/incremental_resolver.dart

 // Copyright (c) 2014, 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 analyzer.src.generated.incremental_resolver;
 
 import 'dart:collection';
 import 'dart:math' as math;
 
 import 'package:analyzer/dart/ast/ast.dart';
@@ skipping 1668 matching lines @@
     incrementalResolver._resolveReferences(newComment);
     // update 'documentationComment' of the parent element(s)
     {
       AstNode parent = newComment.parent;
       if (parent is AnnotatedNode) {
         Element parentElement = ElementLocator.locate(newComment.parent);
         if (parentElement is ElementImpl) {
           setElementDocumentationComment(parentElement, parent);
         } else if (parentElement == null && parent is FieldDeclaration) {
           for (VariableDeclaration field in parent.fields.variables) {
-            if (field.element is ElementImpl) {
-              setElementDocumentationComment(
-                  field.element as ElementImpl, parent);
+            Element fieldElement = field.element;
+            if (fieldElement is ElementImpl) {
+              setElementDocumentationComment(fieldElement, parent);
             }
           }
         }
       }
     }
     // OK
     return true;
   }
 
   Token _scan(String code) {
@@ skipping 157 matching lines @@
   }
 
   static AstNode _findNodeCovering(AstNode root, int offset, int end) {
     NodeLocator nodeLocator = new NodeLocator(offset, end);
     return nodeLocator.searchWithin(root);
   }
 
   static Token _getBeginTokenNotComment(AstNode node) {
     Token oldBeginToken = node.beginToken;
     if (oldBeginToken is CommentToken) {
-      oldBeginToken = (oldBeginToken as CommentToken).parent;
+      return oldBeginToken.parent;
     }
     return oldBeginToken;
   }
 
   static List<AstNode> _getParents(AstNode node) {
     List<AstNode> parents = <AstNode>[];
     while (node != null) {
       parents.insert(0, node);
       node = node.parent;
     }
@@ skipping 356 matching lines @@
   @override
   String toString() => name;
 }
 
 class _TokenPair {
   final _TokenDifferenceKind kind;
   final Token oldToken;
   final Token newToken;
   _TokenPair(this.kind, this.oldToken, this.newToken);
 }