[base/allocator] Refactor allocator.gni, and fix sanitizer detection.

Make sure we don't forget any sanitizer when deciding to not use our own
allocator. HWASAN was missing from an "else" clause, even though it
requires its own allocator.

Reported by bartekn@.

Change-Id: Iecfc14d4a4782ab8c72f8015948afe3cd8485169
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2627155Reviewed-by: Bartek Nowierski <bartekn@chromium.org>
Commit-Queue: Benoit L <lizeb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#843036}

base/allocator/allocator.gni

@@ -5,12 +5,14 @@
 import("//build/config/chromecast_build.gni")
 import("//build/config/sanitizers/sanitizers.gni")
 
+# Sanitizers replace the allocator, don't use our own.
+_is_using_sanitizers = is_asan || is_hwasan || is_lsan || is_tsan || is_msan
+
 # The debug CRT on Windows has some debug features that are incompatible with
 # the shim. NaCl in particular does seem to link some binaries statically
 # against the debug CRT with "is_nacl=false".
 if ((is_linux || is_chromeos || is_android || is_apple ||
-     (is_win && !is_component_build && !is_debug)) && !is_asan && !is_hwasan &&
-    !is_lsan && !is_tsan && !is_msan) {
+     (is_win && !is_component_build && !is_debug)) && !_is_using_sanitizers) {
   _default_use_allocator_shim = true
 } else {
   _default_use_allocator_shim = false
@@ -18,9 +20,8 @@ if ((is_linux || is_chromeos || is_android || is_apple ||
 
 if (_default_use_allocator_shim && is_win) {
   _default_allocator = "partition"
-} else if (is_android || is_apple || is_asan || is_lsan || is_tsan || is_msan ||
-           is_win || is_fuchsia ||
-           ((is_linux || is_chromeos) && target_cpu == "arm64") ||
+} else if (is_android || is_apple || _is_using_sanitizers || is_win ||
+           is_fuchsia || ((is_linux || is_chromeos) && target_cpu == "arm64") ||
            (is_cast_audio_only && target_cpu == "arm")) {
   # Temporarily disable tcmalloc on arm64 linux to get rid of compilation
   # errors.