Enable hermetic build for Google Chrome Mac official.

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

Index: scripts/slave/recipes/chromium.expected/full_chromium_chrome_Google_Chrome_Mac.json
diff --git a/scripts/slave/recipes/chromium.expected/full_chromium_chrome_Google_Chrome_Mac.json b/scripts/slave/recipes/chromium.expected/full_chromium_chrome_Google_Chrome_Mac.json
index 520a590ad32ca8484b79cfb669f6bf1fbd193207..338a1aa0ff609681665ccec5bb87500e3bb91c44 100644
--- a/scripts/slave/recipes/chromium.expected/full_chromium_chrome_Google_Chrome_Mac.json
+++ b/scripts/slave/recipes/chromium.expected/full_chromium_chrome_Google_Chrome_Mac.json
@@ -186,6 +186,7 @@
     ],
     "cwd": "[SLAVE_BUILD]/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": "branding=Chrome buildtype=Official clang=1 component=static_library gomadir='[CACHE]/cipd/goma' target_arch=x64 use_goma=1",
@@ -257,6 +258,7 @@
       "//out/Release"
     ],
     "env": {
+      "FORCE_MAC_TOOLCHAIN": "1",
       "GOMA_SERVICE_ACCOUNT_JSON_FILE": "/creds/service_accounts/service-account-goma-client.json"
     },
     "name": "generate_build_files"
@@ -273,6 +275,7 @@
       "/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",
@@ -319,6 +322,7 @@
       "chrome"
     ],
     "env": {
+      "FORCE_MAC_TOOLCHAIN": "1",
       "GOMA_SERVICE_ACCOUNT_JSON_FILE": "/creds/service_accounts/service-account-goma-client.json"
     },
     "name": "compile",
@@ -357,6 +361,7 @@
       "mac"
     ],
     "env": {
+      "FORCE_MAC_TOOLCHAIN": "1",
       "GOMA_SERVICE_ACCOUNT_JSON_FILE": "/creds/service_accounts/service-account-goma-client.json"
     },
     "name": "sizes"