Include -fsanitize=float-cast-overflow in is_ubsan=true builds.

build/config/sanitizers/BUILD.gn

 # Copyright 2014 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.
 
 import("//build_overrides/build.gni")
 import("//build/config/chrome_build.gni")
 import("//build/config/chromecast_build.gni")
 import("//build/config/clang/clang.gni")
 import("//build/config/sanitizers/sanitizers.gni")
 import("//build/toolchain/toolchain.gni")
@@ skipping 410 matching lines @@
     assert(is_linux, "tsan only supported on linux x86_64")
     tsan_blacklist_path =
         rebase_path("//tools/memory/tsan_v2/ignores.txt", root_build_dir)
     cflags = [
       "-fsanitize=thread",
       "-fsanitize-blacklist=$tsan_blacklist_path",
     ]
   }
 }
 
+# UBSan is still in bring-up.  Chrome builds with is_ubsan=true, but if you
+# set is_ubsan=true is_ubsan_no_recover = true, then many tests are still
+# failing.
 config("ubsan_flags") {
   cflags = []
   if (is_ubsan) {
     ubsan_blacklist_path =
         rebase_path("//tools/ubsan/blacklist.txt", root_build_dir)
     cflags += [
       # Yasm dies with an "Illegal instruction" error when bounds checking is
       # enabled. See http://crbug.com/489901
       # "-fsanitize=bounds",
       "-fsanitize=float-divide-by-zero",
+      "-fsanitize=float-cast-overflow",
       "-fsanitize=integer-divide-by-zero",
       "-fsanitize=null",
       "-fsanitize=object-size",
       "-fsanitize=return",
       "-fsanitize=returns-nonnull-attribute",
       "-fsanitize=shift-exponent",
       "-fsanitize=signed-integer-overflow",
       "-fsanitize=unreachable",
       "-fsanitize=vla-bound",
       "-fsanitize-blacklist=$ubsan_blacklist_path",
@@ skipping 84 matching lines @@
 # This allows to selectively disable ubsan_vptr, when needed. In particular,
 # if some third_party code is required to be compiled without rtti, which
 # is a requirement for ubsan_vptr.
 config("default_sanitizer_flags_but_ubsan_vptr") {
   configs = all_sanitizer_configs - [ ":ubsan_vptr_flags" ]
 }
 
 config("default_sanitizer_flags_but_coverage") {
   configs = all_sanitizer_configs - [ ":coverage_flags" ]
 }