Set using_sanitizer if use_cfi_diag is true.

build/config/sanitizers/BUILD.gn

Index: build/config/sanitizers/BUILD.gn
diff --git a/build/config/sanitizers/BUILD.gn b/build/config/sanitizers/BUILD.gn
index 637fc881174f37fbcf016d8e314c1f3315ba55fb..03890b992cf6b4cc2cb28c2969ee0c47c84a5590 100644
--- a/build/config/sanitizers/BUILD.gn
+++ b/build/config/sanitizers/BUILD.gn
@@ -259,6 +259,8 @@ config("common_sanitizer_flags") {
   # it's explicitly asked for by setting |sanitizer_keep_symbols| to true).
   if (using_sanitizer) {
     assert(is_clang, "sanitizers only supported with clang")
+    assert(!is_official_build, "sanitizers not supported in official builds")
+
     if (!sanitizer_keep_symbols) {
       cflags += [ "-gline-tables-only" ]
     }
@@ -269,11 +271,8 @@ config("common_sanitizer_flags") {
       # of reports to CLs, so turn it on there.
       "-gcolumn-info",
     ]
-  }
 
-  # Common options for AddressSanitizer, LeakSanitizer, ThreadSanitizer,
-  # MemorySanitizer and non-official CFI builds.
-  if (using_sanitizer || (is_cfi && !is_official_build)) {
+    # Disable frame pointer elimination for better stack traces.
     if (is_posix) {
       cflags += [ "-fno-omit-frame-pointer" ]
     } else {