Fix dart2js checked mode in host-checked mode.

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

Index: sdk/lib/_internal/compiler/implementation/ssa/nodes.dart
diff --git a/sdk/lib/_internal/compiler/implementation/ssa/nodes.dart b/sdk/lib/_internal/compiler/implementation/ssa/nodes.dart
index 69e01024303f880e93bb94d4b459fabda04c78ce..611c2a15b44c5740de1f4a406341b3a963ff7dfc 100644
--- a/sdk/lib/_internal/compiler/implementation/ssa/nodes.dart
+++ b/sdk/lib/_internal/compiler/implementation/ssa/nodes.dart
@@ -1127,7 +1127,8 @@ abstract class HInstruction implements Spannable {
     assert(type.kind != TypeKind.TYPE_VARIABLE);
     assert(type.isRaw || type.kind == TypeKind.FUNCTION);
     if (type.treatAsDynamic) return this;
-    ClassElement element = type.element;
+    // The type element is either a class or the void element.
+    Element element = type.element;
     if (identical(element, compiler.objectClass)) return this;
     if (type.kind != TypeKind.INTERFACE) {
       return new HTypeConversion(type, kind, HType.UNKNOWN, this);
@@ -1135,7 +1136,7 @@ abstract class HInstruction implements Spannable {
       // Boolean conversion checks work on non-nullable booleans.
       return new HTypeConversion(type, kind, HType.BOOLEAN, this);
     } else if (kind == HTypeConversion.CHECKED_MODE_CHECK && !type.isRaw) {
-        throw 'creating compound check to $type (this = ${this})';
+      throw 'creating compound check to $type (this = ${this})';
     } else {
       HType subtype = new HType.subtype(element, compiler);
       return new HTypeConversion(type, kind, subtype, this);