Add a check for issue 6530, so that we don't report errors in checked mode on a void return type.

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

Index: sdk/lib/_internal/compiler/implementation/ssa/builder.dart
===================================================================
--- sdk/lib/_internal/compiler/implementation/ssa/builder.dart	(revision 14527)
+++ sdk/lib/_internal/compiler/implementation/ssa/builder.dart	(working copy)
@@ -3459,7 +3459,12 @@
     } else {
       visit(node.expression);
       value = pop();
-      value = potentiallyCheckType(value, returnType);
+      if (returnType == compiler.types.voidType
+          && value is HForeign) {
+        // TODO(6530): remove this check.
+      } else {
+        value = potentiallyCheckType(value, returnType);
+      }
     }
     if (!inliningStack.isEmpty) {
       localsHandler.updateLocal(returnElement, value);