Avoid critical edge on do/while, and do not make handleLoopInfo return conditionnaly false: block b…

sdk/lib/_internal/compiler/implementation/ssa/builder.dart

Index: sdk/lib/_internal/compiler/implementation/ssa/builder.dart
===================================================================
--- sdk/lib/_internal/compiler/implementation/ssa/builder.dart	(revision 15011)
+++ sdk/lib/_internal/compiler/implementation/ssa/builder.dart	(working copy)
@@ -2049,7 +2049,12 @@
       conditionEndBlock = close(
           new HLoopBranch(conditionInstruction, HLoopBranch.DO_WHILE_LOOP));
 
-      conditionEndBlock.addSuccessor(loopEntryBlock);  // The back-edge.
+      HBasicBlock avoidCriticalEdge = addNewBlock();
+      conditionEndBlock.addSuccessor(avoidCriticalEdge);
+      open(avoidCriticalEdge);
+      close(new HGoto());
+      avoidCriticalEdge.addSuccessor(loopEntryBlock); // The back-edge.
+
       conditionExpression =
           new SubExpression(conditionBlock, conditionEndBlock);
     }