Introduce a new gyp flag to warn about to be deprecated APIs

Makefile

 # Copyright 2012 the V8 project authors. All rights reserved.
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #     * Redistributions of source code must retain the above copyright
 #       notice, this list of conditions and the following disclaimer.
 #     * Redistributions in binary form must reproduce the above
 #       copyright notice, this list of conditions and the following
 #       disclaimer in the documentation and/or other materials provided
@@ skipping 127 matching lines @@
 endif
 # regexp=interpreted
 ifeq ($(regexp), interpreted)
   GYPFLAGS += -Dv8_interpreted_regexp=1
 endif
 # i18nsupport=off
 ifeq ($(i18nsupport), off)
   GYPFLAGS += -Dv8_enable_i18n_support=0
   TESTFLAGS += --noi18n
 endif
-# deprecation_warnings=on
+# deprecationwarnings=on
 ifeq ($(deprecationwarnings), on)
   GYPFLAGS += -Dv8_deprecation_warnings=1
 endif
+# imminentdeprecationwarnings=on
+ifeq ($(imminentdeprecationwarnings), on)
+  GYPFLAGS += -Dv8_imminent_deprecation_warnings=1
+endif
 # asan=on
 ifeq ($(asan), on)
   GYPFLAGS += -Dasan=1 -Dclang=1
   TESTFLAGS += --asan
   ifeq ($(lsan), on)
     GYPFLAGS += -Dlsan=1
   endif
 endif
 ifdef embedscript
   GYPFLAGS += -Dembed_script=$(embedscript)
@@ skipping 333 matching lines @@
 # We need to manually set the stack limit here, to work around bugs in
 # gmake-3.81 and global-5.7.1 on recent 64-bit Linux systems.
 GPATH GRTAGS GSYMS GTAGS: gtags.files $(shell cat gtags.files 2> /dev/null)
         @bash -c 'ulimit -s 10240 && GTAGSFORCECPP=yes gtags -i -q -f $<'
 
 gtags.clean:
         rm -f gtags.files GPATH GRTAGS GSYMS GTAGS
 
 dependencies builddeps:
         $(error Use 'gclient sync' instead)