dart2js: Insert HTypeKnown refinement nodes on dominated edges of HPhi nodes.

pkg/compiler/lib/src/ssa/types_propagation.dart

Index: pkg/compiler/lib/src/ssa/types_propagation.dart
diff --git a/pkg/compiler/lib/src/ssa/types_propagation.dart b/pkg/compiler/lib/src/ssa/types_propagation.dart
index 5b1473a762adc9f103ad32226529370853bdb82b..891d9d6bb6fae9652fdfdcc08f1e27feab5c97cc 100644
--- a/pkg/compiler/lib/src/ssa/types_propagation.dart
+++ b/pkg/compiler/lib/src/ssa/types_propagation.dart
@@ -396,7 +396,9 @@ class SsaTypePropagator extends HBaseVisitor implements OptimizationPhase {
           addDependentInstructionsToWorkList(next);
         }
       } else {
-        bool hasCandidates() => receiver.dominatedUsers(instruction).length > 1;
+        bool hasCandidates() => DominatedUses
+            .of(receiver, instruction, excludeDominator: true)
+            .isNotEmpty;
 
         if ((receiver.usedBy.length <= _MAX_QUICK_USERS)
             ? (hasCandidates() && computeNewType() != receiverType)