build: make pyyaml an optional dependency (electron#15565)

.circleci/config.yml

@@ -721,14 +721,16 @@ jobs:
       GCLIENT_EXTRA_ARGS: '--custom-var=checkout_arm=True --custom-var=checkout_arm64=True'
     <<: *steps-checkout
 
-  linux-x64-checkout:
+  linux-checkout-for-native-tests:
     <<: *machine-linux-2xlarge
+    environment:
+      GCLIENT_EXTRA_ARGS: '--custom-var=checkout_pyyaml=True'
     <<: *steps-checkout
 
-  linux-x64-checkout-no-patches:
+  linux-checkout-for-native-tests-with-no-patches:
     <<: *machine-linux-2xlarge
     environment:
-      GCLIENT_EXTRA_ARGS: '--custom-var=apply_patches=False'
+      GCLIENT_EXTRA_ARGS: '--custom-var=apply_patches=False --custom-var=checkout_pyyaml=True'
     <<: *steps-checkout
 
   # Layer 2: Builds.
@@ -1247,25 +1249,25 @@ workflows:
                 - master
                 - *chromium-upgrade-branches
     jobs:
-      - linux-x64-checkout
+      - linux-checkout-for-native-tests
 
       # TODO(alexeykuzmin): Enable it back.
       # Tons of crashes right now, see
       # https://circleci.com/gh/electron/electron/67463
 #      - linux-x64-browsertests:
 #          requires:
-#            - linux-x64-checkout
+#            - linux-checkout-for-native-tests
 
       - linux-x64-unittests:
           requires:
-            - linux-x64-checkout
+            - linux-checkout-for-native-tests
 
       - linux-x64-disabled-unittests:
           requires:
-            - linux-x64-checkout
+            - linux-checkout-for-native-tests
 
-      - linux-x64-checkout-no-patches
+      - linux-checkout-for-native-tests-with-no-patches
 
       - linux-x64-chromium-unittests:
           requires:
-            - linux-x64-checkout-no-patches
+            - linux-checkout-for-native-tests-with-no-patches

DEPS

@@ -34,6 +34,9 @@ vars = {
   'checkout_chromium': True,
   'checkout_node': True,
 
+  # It's only needed to parse the native tests configurations.
+  'checkout_pyyaml': False,
+
   # Python "requests" module is used for releases only.
   'checkout_requests': False,
 
@@ -64,8 +67,10 @@ deps = {
     'url': (Var("electron_git")) + '/node.git@' + (Var("node_version")),
     'condition': 'checkout_node',
   },
-  'src/electron/vendor/pyyaml':
-    (Var("yaml_git")) + '/pyyaml.git@' + (Var("pyyaml_version")),
+  'src/electron/vendor/pyyaml': {
+    'url': (Var("yaml_git")) + '/pyyaml.git@' + (Var("pyyaml_version")),
+    'condition': 'checkout_pyyaml',
+  },
   'src/electron/vendor/boto': {
     'url': Var('boto_git') + '/boto.git' + '@' +  Var('boto_version'),
     'condition': 'checkout_boto',