Fix some editor warnings.

lib/compiler/implementation/ssa/nodes.dart

 // Copyright (c) 2011, 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.
 
 interface HVisitor<R> {
   R visitAdd(HAdd node);
   R visitBitAnd(HBitAnd node);
   R visitBitNot(HBitNot node);
   R visitBitOr(HBitOr node);
   R visitBitXor(HBitXor node);
@@ skipping 2366 matching lines @@
 
   HBasicBlock get start() => body.start;
   HBasicBlock get end() => body.end;
 
   bool accept(HStatementInformationVisitor visitor) =>
     visitor.visitLabeledBlockInfo(this);
 }
 
 class LoopTypeVisitor extends AbstractVisitor {
   const LoopTypeVisitor();
-  int visitNode(Node node) {
-    // TODO(lrn): Need a compiler object here.
-    compiler.internalError('visitNode should not be called', node: node);
-  }
+  int visitNode(Node node) => HLoopBlockInformation.NOT_A_LOOP;
   int visitWhile(While node) => HLoopBlockInformation.WHILE_LOOP;
   int visitFor(For node) => HLoopBlockInformation.FOR_LOOP;
   int visitDoWhile(DoWhile node) => HLoopBlockInformation.DO_WHILE_LOOP;
   int visitForIn(ForIn node) => HLoopBlockInformation.FOR_IN_LOOP;
 }
 
 class HLoopBlockInformation implements HStatementInformation {
   static final int WHILE_LOOP = 0;
   static final int FOR_LOOP = 1;
   static final int DO_WHILE_LOOP = 2;
   static final int FOR_IN_LOOP = 3;
+  static final int NOT_A_LOOP = -1;
 
   final int kind;
   final HExpressionInformation initializer;
   final HExpressionInformation condition;
   final HStatementInformation body;
   final HExpressionInformation updates;
   final TargetElement target;
   final List<LabelElement> labels;
 
   HLoopBlockInformation(this.kind,
@@ skipping 49 matching lines @@
   final HExpressionInformation right;
   HAndOrBlockInformation(this.isAnd,
                          this.left,
                          this.right);
 
   HBasicBlock get start() => left.start;
   HBasicBlock get end() => right.end;
 
   // We don't currently use HAndOrBlockInformation.
   HInstruction get conditionExpression() {
-    // TODO(lrn): Need a compiler object.
-    compiler.internalError('conditionExpression should not be called',
-                           instruction: this);
+    return null;
   }
   bool accept(HExpressionInformationVisitor visitor) =>
     visitor.visitAndOrInfo(this);
 }
 
 class HTryBlockInformation implements HStatementInformation {
   final HStatementInformation body;
   final HParameterValue catchVariable;
   final HStatementInformation catchBlock;
   final HStatementInformation finallyBlock;
   HTryBlockInformation(this.body,
                        this.catchVariable,
                        this.catchBlock,
                        this.finallyBlock);
 
   HBasicBlock get start() => body.start;
   HBasicBlock get end() =>
       finallyBlock === null ? catchBlock.end : finallyBlock.end;
 
   bool accept(HStatementInformationVisitor visitor) =>
     visitor.visitTryInfo(this);
 }