Add back a dummy --harmony-promises flag

This is mainly meant to help with the transition of chrome using the
flag to promises being enabled by default

BUG=none
LOG=n
R=rossberg@chromium.org, svenpanne@chromium.org

Review URL: https://codereview.chromium.org/270503005

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21188 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/flag-definitions.h

@@ -162,6 +162,7 @@ DEFINE_bool(harmony_numeric_literals, false,
 DEFINE_bool(harmony_strings, false, "enable harmony string")
 DEFINE_bool(harmony_arrays, false, "enable harmony arrays")
 DEFINE_bool(harmony_maths, false, "enable harmony math functions")
+DEFINE_bool(harmony_promises, true, "(dummy flag, has no effect)")
 DEFINE_bool(harmony, false, "enable all harmony features (except typeof)")
 
 DEFINE_implication(harmony, harmony_scoping)