[libfuzzer] separate libfuzzer ubsan configuration and ubsan build config setup.

build/config/sanitizers/sanitizers.gni

 # Copyright 2015 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 declare_args() {
   # Compile for Address Sanitizer to find memory bugs.
   is_asan = false
 
   # Compile for Leak Sanitizer to find leaks.
   is_lsan = false
@@ skipping 31 matching lines @@
   is_cfi = false
 
   # By default, Control Flow Integrity will crash the program if it detects a
   # violation. Set this to true to print detailed diagnostics instead.
   use_cfi_diag = false
 
   # Compile for fuzzing with LLVM LibFuzzer.
   # See http://www.chromium.org/developers/testing/libfuzzer
   use_libfuzzer = false
 
+  # Separate configuration for libfuzzer ubsan build. Used to deploy ubsan
+  # gradually. Eventually should catch up with is_ubsan and should be removed.

[inferno, 2016/03/25 20:57:55]

Can you fix the comment to indicate this is a flag that enable some core
security features instead and will later be removed.

[aizatsky, 2016/03/25 21:02:45]

Done.

+  is_libfuzzer_ubsan = false
+
   # Compile for fuzzing with Dr. Fuzz
   # See http://www.chromium.org/developers/testing/dr-fuzz
   use_drfuzz = false
 
   # Helper variable for testing builds with disabled libfuzzer.
   # Not for client use.
   disable_libfuzzer = false
 }
 
 # Args that are in turn dependent on other args must be in a separate
@@ skipping 28 matching lines @@
 # If you find a use-case where you want to compile a sanitizer in debug mode
 # and have verified it works, ask brettw and we can consider removing it from
 # this condition. We may also be able to find another way to enable your case
 # without having people accidentally get broken builds by compiling an
 # unsupported or unadvisable configurations.
 #
 # For one-off testing, just comment this assertion out.
 assert(
     !is_debug || !(is_msan || is_lsan || is_tsan || is_ubsan || is_ubsan_vptr),
     "Sanitizers should generally be used in release (set is_debug=false).")