[strong] deprecate empty sub-statements

src/messages.js

Index: src/messages.js
diff --git a/src/messages.js b/src/messages.js
index 12700130f84a8b17d49a4635132946dfde72e466..b554175bccf21b27e295adb7517c192566a0a01e 100644
--- a/src/messages.js
+++ b/src/messages.js
@@ -164,6 +164,8 @@ var kMessages = {
   strong_equal:                  ["Please don't use '==' or '!=' in strong mode, use '===' or '!==' instead"],
   strong_delete:                 ["Please don't use 'delete' in strong mode, use maps or sets instead"],
   strong_var:                    ["Please don't use 'var' in strong mode, use 'let' or 'const' instead"],
+  strong_empty:                  ["Please don't use empty sub-statements in strong mode, make them explicit with '{}' instead"],
+  sloppy_lexical:                ["Block-scoped declarations (let, const, function, class) not yet supported outside strict mode"],
   malformed_arrow_function_parameter_list: ["Malformed arrow function parameter list"],
   generator_poison_pill:         ["'caller' and 'arguments' properties may not be accessed on generator functions."],
   cant_prevent_ext_external_array_elements: ["Cannot prevent extension of an object with external array elements"],
@@ -179,7 +181,6 @@ var kMessages = {
   extends_value_not_a_function:  ["Class extends value ", "%0", " is not a function or null"],
   prototype_parent_not_an_object: ["Class extends value does not have valid prototype property ", "%0"],
   duplicate_constructor:         ["A class may only have one constructor"],
-  sloppy_lexical:                ["Block-scoped declarations (let, const, function, class) not yet supported outside strict mode"],
   super_constructor_call:        ["A 'super' constructor call may only appear as the first statement of a function, and its arguments may not access 'this'. Other forms are not yet supported."],
   duplicate_proto:               ["Duplicate __proto__ fields are not allowed in object literals"],
   param_after_rest:              ["Rest parameter must be last formal parameter"],