Implement use_cfi_cast to optionally enable cast checks.

base/BUILD.gn

 # Copyright (c) 2013 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.
 
 # HOW TO WRITE CONDITIONALS IN THIS FILE
 # ======================================
 #
 # In many other places, one would write a conditional that expresses all the
 # cases when a source file is used or unused, and then either add or subtract
 # it from the sources list in that case
@@ skipping 1961 matching lines @@
     "win/scoped_process_information_unittest.cc",
     "win/scoped_variant_unittest.cc",
     "win/shortcut_unittest.cc",
     "win/startup_information_unittest.cc",
     "win/wait_chain_unittest.cc",
     "win/win_util_unittest.cc",
     "win/windows_version_unittest.cc",
     "win/wrapped_window_proc_unittest.cc",
   ]
 
+  defines = []
+
   deps = [
     ":base",
     ":i18n",
     ":message_loop_tests",
     "//base/test:run_all_unittests",
     "//base/test:test_support",
     "//base/third_party/dynamic_annotations",
     "//testing/gmock",
     "//testing/gtest",
     "//third_party/icu",
@@ skipping 10 matching lines @@
   # Some unittests depend on the ALLOCATOR_SHIM macro.
   configs += [ "//base/allocator:allocator_shim_define" ]
 
   data = [
     "test/data/",
   ]
 
   # Allow more direct string conversions on platforms with native utf8
   # strings
   if (is_mac || is_ios || is_chromeos || is_chromecast) {
-    defines = [ "SYSTEM_NATIVE_UTF8" ]
+    defines += [ "SYSTEM_NATIVE_UTF8" ]
   }
 
   if (is_android) {
     deps += [
       ":base_java",
       ":base_java_unittest_support",
       "//base/android/jni_generator:jni_generator_tests",
     ]
   }
 
@@ skipping 84 matching lines @@
 
   # Symbols for crashes when running tests on swarming.
   if (symbol_level > 0) {
     if (is_win) {
       data += [ "$root_out_dir/base_unittests.exe.pdb" ]
     } else if (is_mac) {
       # TODO(crbug.com/330301): make this conditional on mac_strip_release.
       # data += [ "$root_out_dir/base_unittests.dSYM/" ]
     }
   }
+
+  if (use_cfi_cast) {
+    # TODO(krasin): remove CFI_CAST_CHECK, see https://crbug.com/626794.
+    defines += [ "CFI_CAST_CHECK" ]
+  }
 }
 
 action("build_date") {
   script = "//build/write_build_date_header.py"
 
   # Force recalculation if there's been a change.
   inputs = [
     "//build/util/LASTCHANGE",
   ]
   outputs = [
@@ skipping 290 matching lines @@
 
   # GYP: //base.gyp:base_java_unittest_support
   android_library("base_java_unittest_support") {
     deps = [
       ":base_java",
     ]
     java_files =
         [ "test/android/java/src/org/chromium/base/ContentUriTestUtils.java" ]
   }
 }