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

scripts/slave/recipes/chromium.expected/full_chromium_webkit_WebKit_Mac10_11__dbg_.json

Index: scripts/slave/recipes/chromium.expected/full_chromium_webkit_WebKit_Mac10_11__dbg_.json
diff --git a/scripts/slave/recipes/chromium.expected/full_chromium_webkit_WebKit_Mac10_11__dbg_.json b/scripts/slave/recipes/chromium.expected/full_chromium_webkit_WebKit_Mac10_11__dbg_.json
index d34e40f53560f4d6f05e9c747ea787d07553bfd7..7828e39bb257c31b72c7b4e9b7cebdcce820653b 100644
--- a/scripts/slave/recipes/chromium.expected/full_chromium_webkit_WebKit_Mac10_11__dbg_.json
+++ b/scripts/slave/recipes/chromium.expected/full_chromium_webkit_WebKit_Mac10_11__dbg_.json
@@ -200,6 +200,7 @@
     ],
     "cwd": "[BUILDER_CACHE]/mac_layout/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": "clang=1 component=shared_library gomadir='[CACHE]/cipd/goma' target_arch=x64 test_isolation_mode=prepare use_goma=1",
@@ -319,6 +320,7 @@
     ],
     "cwd": "[BUILDER_CACHE]/mac_layout",
     "env": {
+      "FORCE_MAC_TOOLCHAIN": "1",
       "GOMA_SERVICE_ACCOUNT_JSON_FILE": "/creds/service_accounts/service-account-goma-client.json"
     },
     "name": "find isolated tests",
@@ -396,6 +398,7 @@
     ],
     "cwd": "[BUILDER_CACHE]/mac_layout",
     "env": {
+      "FORCE_MAC_TOOLCHAIN": "1",
       "GOMA_SERVICE_ACCOUNT_JSON_FILE": "/creds/service_accounts/service-account-goma-client.json"
     },
     "name": "[trigger] browser_tests on Mac-10.11",
@@ -450,6 +453,7 @@
     ],
     "cwd": "[BUILDER_CACHE]/mac_layout",
     "env": {
+      "FORCE_MAC_TOOLCHAIN": "1",
       "GOMA_SERVICE_ACCOUNT_JSON_FILE": "/creds/service_accounts/service-account-goma-client.json"
     },
     "name": "webkit_tests",
@@ -479,6 +483,7 @@
     ],
     "cwd": "[BUILDER_CACHE]/mac_layout",
     "env": {
+      "FORCE_MAC_TOOLCHAIN": "1",
       "GOMA_SERVICE_ACCOUNT_JSON_FILE": "/creds/service_accounts/service-account-goma-client.json"
     },
     "name": "archive_webkit_tests_results",
@@ -512,6 +517,7 @@
     ],
     "cwd": "[BUILDER_CACHE]/mac_layout",
     "env": {
+      "FORCE_MAC_TOOLCHAIN": "1",
       "GOMA_SERVICE_ACCOUNT_JSON_FILE": "/creds/service_accounts/service-account-goma-client.json"
     },
     "name": "browser_tests on Mac-10.11",
@@ -541,6 +547,7 @@
     ],
     "cwd": "[BUILDER_CACHE]/mac_layout",
     "env": {
+      "FORCE_MAC_TOOLCHAIN": "1",
       "GOMA_SERVICE_ACCOUNT_JSON_FILE": "/creds/service_accounts/service-account-goma-client.json"
     },
     "name": "Upload to test-results [browser_tests on Mac-10.11]"