Download the hermetic xcode toolchain on all bots that target mac.

scripts/slave/recipes/chromium.expected/full_chromium_memory_Mac_ASan_64_Builder.json

Index: scripts/slave/recipes/chromium.expected/full_chromium_memory_Mac_ASan_64_Builder.json
diff --git a/scripts/slave/recipes/chromium.expected/full_chromium_memory_Mac_ASan_64_Builder.json b/scripts/slave/recipes/chromium.expected/full_chromium_memory_Mac_ASan_64_Builder.json
index 3f308a3dbfeaba1cdca38a34b8834b92b4b052f7..9d279e655a1ce29ede54639d0d26d6b51cf23067 100644
--- a/scripts/slave/recipes/chromium.expected/full_chromium_memory_Mac_ASan_64_Builder.json
+++ b/scripts/slave/recipes/chromium.expected/full_chromium_memory_Mac_ASan_64_Builder.json
@@ -200,6 +200,7 @@
     ],
     "cwd": "[BUILDER_CACHE]/mac_ng/src",
     "env": {
+      "FORCE_MAC_TOOLCHAIN": "1",
       "GOMA_SERVICE_ACCOUNT_JSON_FILE": "/creds/service_accounts/service-account-goma-client.json",
       "GYP_CHROMIUM_NO_ACTION": "1",
       "GYP_DEFINES": "asan=1 clang=1 component=static_library fastbuild=0 gomadir='[CACHE]/cipd/goma' host_arch=x64 target_arch=x64 test_isolation_mode=prepare use_goma=1",
@@ -297,6 +298,7 @@
     ],
     "cwd": "[BUILDER_CACHE]/mac_ng/src",
     "env": {
+      "FORCE_MAC_TOOLCHAIN": "1",
       "GOMA_SERVICE_ACCOUNT_JSON_FILE": "/creds/service_accounts/service-account-goma-client.json"
     },
     "name": "generate_build_files",
@@ -317,6 +319,7 @@
       "/path/to/tmp/json"
     ],
     "env": {
+      "FORCE_MAC_TOOLCHAIN": "1",
       "GOMA_SERVICE_ACCOUNT_JSON_FILE": "/creds/service_accounts/service-account-goma-client.json"
     },
     "name": "clang_revision",
@@ -368,6 +371,7 @@
       "browser_tests_run"
     ],
     "env": {
+      "FORCE_MAC_TOOLCHAIN": "1",
       "GOMA_SERVICE_ACCOUNT_JSON_FILE": "/creds/service_accounts/service-account-goma-client.json"
     },
     "name": "compile",