Detect total switches to prevent type pollution by default cases.

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

Index: sdk/lib/_internal/compiler/implementation/ssa/tracer.dart
diff --git a/sdk/lib/_internal/compiler/implementation/ssa/tracer.dart b/sdk/lib/_internal/compiler/implementation/ssa/tracer.dart
index 37731ba36fd9bd7429291f6ceb9226e910ff285a..c8d9e45aea5e3a8e0ca9b68b8ac9dea8929625ec 100644
--- a/sdk/lib/_internal/compiler/implementation/ssa/tracer.dart
+++ b/sdk/lib/_internal/compiler/implementation/ssa/tracer.dart
@@ -466,7 +466,7 @@ class HInstructionStringifier implements HVisitor<String> {
       buf.write(", ");
     }
     buf.write("default: B");
-    buf.write(node.block.successors.last.id);
+    buf.write(node.defaultTarget.id);
     return buf.toString();
   }