Reland of [es6] ship regexp sticky flag. (patchset #1 id:1 of...

Reland of [es6] ship regexp sticky flag. (patchset #1 id:1 of https://codereview.chromium.org/1531043002/ )

Reason for revert:
This can be relanded since the web compatibility fix in https://codereview.chromium.org/1543723002 has been submitted.

Original issue's description:
> Revert of [es6] ship regexp sticky flag. (patchset #2 id:20001 of https://codereview.chromium.org/1509733010/ )
>
> Reason for revert:
> This causes compatibility issues, as documented in https://bugs.chromium.org/p/v8/issues/detail?id=4617#c9
>
> Original issue's description:
> > [es6] ship regexp sticky flag.
> >
> > R=littledan@chromium.org
> > BUG=v8:4342
> > LOG=Y
> >
> > Committed: https://crrev.com/86c2dd4042dc9ce293e004234eb094f2b51d9640
> > Cr-Commit-Position: refs/heads/master@{#32826}
>
> TBR=yangguo@chromium.org
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> BUG=v8:4342

TBR=yangguo@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=v8:4342

Review URL: https://codereview.chromium.org/1546563002

Cr-Commit-Position: refs/heads/master@{#33003}

src/flag-definitions.h

@@ -214,7 +214,6 @@ DEFINE_IMPLICATION(es_staging, harmony_regexp_lookbehind)
   V(harmony_sloppy, "harmony features in sloppy mode")                    \
   V(harmony_sloppy_let, "harmony let in sloppy mode")                     \
   V(harmony_sloppy_function, "harmony sloppy function block scoping")     \
-  V(harmony_regexps, "harmony regular expression extensions")             \
   V(harmony_regexp_lookbehind, "harmony regexp lookbehind")
 
 // Features that are shipping (turned on by default, but internal flag remains).
@@ -225,7 +224,8 @@ DEFINE_IMPLICATION(es_staging, harmony_regexp_lookbehind)
   V(harmony_object_observe, "harmony Object.observe")         \
   V(harmony_tolength, "harmony ToLength")                     \
   V(harmony_tostring, "harmony toString")                     \
-  V(harmony_completion, "harmony completion value semantics")
+  V(harmony_completion, "harmony completion value semantics") \
+  V(harmony_regexps, "harmony regular expression extensions")
 
 
 // Once a shipping feature has proved stable in the wild, it will be dropped