Change interfaces to abstract classes in dart2js compiler.

lib/compiler/implementation/ssa/nodes.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.
 
-interface HVisitor<R> {
+abstract class HVisitor<R> {
   R visitAdd(HAdd node);
   R visitBailoutTarget(HBailoutTarget node);
   R visitBitAnd(HBitAnd node);
   R visitBitNot(HBitNot node);
   R visitBitOr(HBitOr node);
   R visitBitXor(HBitXor node);
   R visitBoolify(HBoolify node);
   R visitBoundsCheck(HBoundsCheck node);
   R visitBreak(HBreak node);
   R visitConstant(HConstant node);
@@ skipping 2618 matching lines @@
 class HBlockFlow {
   final HBlockInformation body;
   final HBasicBlock continuation;
   HBlockFlow(this.body, this.continuation);
 }
 
 
 /**
  * Information about a syntactic-like structure.
  */
-interface HBlockInformation {
+abstract class HBlockInformation {
   HBasicBlock get start;
   HBasicBlock get end;
   bool accept(HBlockInformationVisitor visitor);
 }
 
 
 /**
  * Information about a statement-like structure.
  */
-interface HStatementInformation extends HBlockInformation {
+abstract class HStatementInformation extends HBlockInformation {
   bool accept(HStatementInformationVisitor visitor);
 }
 
 
 /**
  * Information about an expression-like structure.
  */
-interface HExpressionInformation extends HBlockInformation {
+abstract class HExpressionInformation extends HBlockInformation {
   bool accept(HExpressionInformationVisitor visitor);
   HInstruction get conditionExpression;
 }
 
 
-interface HStatementInformationVisitor {
+abstract class HStatementInformationVisitor {
   bool visitLabeledBlockInfo(HLabeledBlockInformation info);
   bool visitLoopInfo(HLoopBlockInformation info);
   bool visitIfInfo(HIfBlockInformation info);
   bool visitTryInfo(HTryBlockInformation info);
   bool visitSwitchInfo(HSwitchBlockInformation info);
   bool visitSequenceInfo(HStatementSequenceInformation info);
   // Pseudo-structure embedding a dominator-based traversal into
   // the block-structure traversal. This will eventually go away.
   bool visitSubGraphInfo(HSubGraphBlockInformation info);
 }
 
 
-interface HExpressionInformationVisitor {
+abstract class HExpressionInformationVisitor {
   bool visitAndOrInfo(HAndOrBlockInformation info);
   bool visitSubExpressionInfo(HSubExpressionBlockInformation info);
 }
 
 
-interface HBlockInformationVisitor extends HStatementInformationVisitor,
-                                           HExpressionInformationVisitor {
+abstract class HBlockInformationVisitor
+    implements HStatementInformationVisitor, HExpressionInformationVisitor {
 }
 
 
 /**
  * Generic class wrapping a [SubGraph] as a block-information until
  * all structures are handled properly.
  */
 class HSubGraphBlockInformation implements HStatementInformation {
   final SubGraph subGraph;
   HSubGraphBlockInformation(this.subGraph);
@@ skipping 198 matching lines @@
   HBasicBlock get start => expression.start;
   HBasicBlock get end {
     // We don't create a switch block if there are no cases.
     assert(!statements.isEmpty());
     return statements.last().end;
   }
 
   bool accept(HStatementInformationVisitor visitor) =>
       visitor.visitSwitchInfo(this);
 }