Fix a crash in the compiler where an ssa instruction was using itself.

sdk/lib/_internal/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.
 
 part of ssa;
 
 abstract class HVisitor<R> {
   R visitAdd(HAdd node);
   R visitBailoutTarget(HBailoutTarget node);
   R visitBitAnd(HBitAnd node);
@@ skipping 1100 matching lines @@
   /**
    * The code for computing a bailout environment, and the code
    * generation must agree on what does not need to be captured,
    * so should always be generated at use site.
    */
   bool isCodeMotionInvariant() => false;
 
   bool isJsStatement(HTypeMap types) => false;
 
   bool dominates(HInstruction other) {
+    // An instruction does not dominates itself.
+    if (this == other) return false;
     if (block != other.block) return block.dominates(other.block);
 
-    HInstruction current = this;
+    HInstruction current = this.next;
     while (current != null) {
-      if (identical(current, other)) return true;
+      if (current == other) return true;
       current = current.next;
     }
     return false;
   }
 
 
   HInstruction convertType(Compiler compiler, DartType type, int kind) {
     if (type == null) return this;
     if (identical(type.element, compiler.dynamicClass)) return this;
     if (identical(type.element, compiler.objectClass)) return this;
@@ skipping 1878 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);
 }