Fix crash in compiler when we are generating a bailout method where a loop contains continue/break/…

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 2571 matching lines @@
   final SourceFileLocation endSourcePosition;
 
   HLoopBlockInformation(this.kind,
                         this.initializer,
                         this.condition,
                         this.body,
                         this.updates,
                         this.target,
                         this.labels,
                         this.sourcePosition,
-                        this.endSourcePosition);
+                        this.endSourcePosition) {
+    assert(
+        (kind == DO_WHILE_LOOP ? body.start : condition.start).isLoopHeader());
+  }
 
   HBasicBlock get start {
     if (initializer != null) return initializer.start;
     if (kind == DO_WHILE_LOOP) {
       return body.start;
     }
     return condition.start;
   }
 
   HBasicBlock get loopHeader {
@@ skipping 90 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);
 }