Don't allow statement-nodes in expression contexts.

lib/compiler/implementation/ssa/optimize.dart

Index: lib/compiler/implementation/ssa/optimize.dart
diff --git a/lib/compiler/implementation/ssa/optimize.dart b/lib/compiler/implementation/ssa/optimize.dart
index c19202f4477c2d68714b1786bcc35f83c30cd835..27e382d4f6ac06bdf638c29d19c2a379134958bc 100644
--- a/lib/compiler/implementation/ssa/optimize.dart
+++ b/lib/compiler/implementation/ssa/optimize.dart
@@ -70,7 +70,7 @@ class SsaOptimizerTask extends CompilerTask {
       // In order to generate correct code for the bailout version, we did not
       // propagate types from the instruction to the type guard. We do it
       // now to be able to optimize further.
-      work.guards.forEach((HTypeGuard guard) { guard.isOn = true; });
+      work.guards.forEach((HTypeGuard guard) { guard.isEnabled = true; });
       // We also need to insert range and integer checks for the type
       // guards. Now that they claim to have a certain type, some
       // depending instructions might become builtin (like native array