Don't allow statement-nodes in expression contexts.

lib/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.
 
 interface HVisitor<R> {
   R visitAdd(HAdd node);
   R visitBitAnd(HBitAnd node);
   R visitBitNot(HBitNot node);
   R visitBitOr(HBitOr node);
   R visitBitXor(HBitXor node);
@@ skipping 974 matching lines @@
 /**
  * A [HCheck] instruction is an instruction that might do a dynamic
  * check at runtime on another instruction. To have proper instruction
  * dependencies in the graph, instructions that depend on the check
  * being done reference the [HCheck] instruction instead of the
  * instruction itself.
  */
 abstract class HCheck extends HInstruction {
   HCheck(inputs) : super(inputs);
   HInstruction get checkedInput() => inputs[0];
-  final bool isStatement = true;
+  bool get isStatement() => true;
   void prepareGvn() {
     assert(!hasSideEffects());
     setUseGvn();
   }
 }
 
 class HTypeGuard extends HCheck {
   final int state;
   final HType guardedType;
-  bool isOn = false;
+  bool isEnabled = false;
   int checkedInputIndex = 0;
 
   HTypeGuard(this.guardedType, this.state, List<HInstruction> env) : super(env);
 
   HInstruction get guarded() => inputs[checkedInputIndex];
   HInstruction get checkedInput() => guarded;
 
   HType computeTypeFromInputTypes() {
-    return isOn ? guardedType : guarded.propagatedType;
+    return isEnabled ? guardedType : guarded.propagatedType;
   }
 
-  HType get guaranteedType() => isOn ? guardedType : HType.UNKNOWN;
+  HType get guaranteedType() => isEnabled ? guardedType : HType.UNKNOWN;
 
   bool isControlFlow() => true;
 
+  bool get isStatement() => isEnabled;
+
   accept(HVisitor visitor) => visitor.visitTypeGuard(this);
   int typeCode() => 1;
   bool typeEquals(other) => other is HTypeGuard;
   bool dataEquals(HTypeGuard other) {
     return guarded == other.guarded && guardedType == other.guardedType;
   }
 }
 
 class HBoundsCheck extends HCheck {
   static final int ALWAYS_FALSE = 0;
@@ skipping 1596 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);
 }