[regexp] Stage the dotall flag

BUG=v8:6172

Review-Url: https://codereview.chromium.org/2795693002
Cr-Commit-Position: refs/heads/master@{#44360}

src/flag-definitions.h

@@ -199,7 +199,6 @@ DEFINE_IMPLICATION(es_staging, harmony)
   V(harmony_tailcalls, "harmony tail calls")                            \
   V(harmony_sharedarraybuffer, "harmony sharedarraybuffer")             \
   V(harmony_do_expressions, "harmony do-expressions")                   \
-  V(harmony_regexp_dotall, "harmony regexp dotall flag")                \
   V(harmony_regexp_property, "harmony unicode regexp property classes") \
   V(harmony_class_fields, "harmony public fields in class literals")    \
   V(harmony_async_iteration, "harmony async iteration")                 \
@@ -209,6 +208,7 @@ DEFINE_IMPLICATION(es_staging, harmony)
 // Features that are complete (but still behind --harmony/es-staging flag).
 #define HARMONY_STAGED(V)                                                \
   V(harmony_function_tostring, "harmony Function.prototype.toString")    \
+  V(harmony_regexp_dotall, "harmony regexp dotall flag")                 \
   V(harmony_regexp_lookbehind, "harmony regexp lookbehind")              \
   V(harmony_regexp_named_captures, "harmony regexp named captures")      \
   V(harmony_restrictive_generators,                                      \

test/mjsunit/harmony/regexp-dotall-disabled.js

@@ -5,6 +5,8 @@
 // This tests that RegExp dotall features are not enabled when
 // --harmony-regexp-dotall is not passed.
 
+// Flags: --no-harmony-regexp-dotall
+
 // Construction does not throw.
 {
   assertThrows("/./s", SyntaxError);