use python3 for gn builders

This is phase 2 in http://shortn/_mycVTm6OEC

Bug: 283
Change-Id: Iafb5f548aabe52255b8e572427ce79158162e5c8
Reviewed-on: https://gn-review.googlesource.com/c/gn/+/13440
Reviewed-by: Brett Wilson <brettw@chromium.org>
Commit-Queue: Takuto Ikuta <tikuta@google.com>
diff --git a/infra/config/generated/cr-buildbucket.cfg b/infra/config/generated/cr-buildbucket.cfg
index 98bdf26..727d9a5 100644
--- a/infra/config/generated/cr-buildbucket.cfg
+++ b/infra/config/generated/cr-buildbucket.cfg
@@ -23,6 +23,10 @@
       }
       execution_timeout_secs: 3600
       service_account: "gn-ci-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.recipes.use_python3"
+        value: 100
+      }
     }
     builders {
       name: "mac"
@@ -41,6 +45,10 @@
         path: "macos_sdk"
       }
       service_account: "gn-ci-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.recipes.use_python3"
+        value: 100
+      }
     }
     builders {
       name: "win"
@@ -59,6 +67,10 @@
         path: "windows_sdk"
       }
       service_account: "gn-ci-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.recipes.use_python3"
+        value: 100
+      }
     }
   }
 }
@@ -89,6 +101,10 @@
       }
       execution_timeout_secs: 3600
       service_account: "gn-try-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.recipes.use_python3"
+        value: 100
+      }
     }
     builders {
       name: "mac"
@@ -107,6 +123,10 @@
         path: "macos_sdk"
       }
       service_account: "gn-try-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.recipes.use_python3"
+        value: 100
+      }
     }
     builders {
       name: "win"
@@ -125,6 +145,10 @@
         path: "windows_sdk"
       }
       service_account: "gn-try-builder@chops-service-accounts.iam.gserviceaccount.com"
+      experiments {
+        key: "luci.recipes.use_python3"
+        value: 100
+      }
     }
   }
 }
diff --git a/infra/config/main.star b/infra/config/main.star
index 7985762..c896dfc 100755
--- a/infra/config/main.star
+++ b/infra/config/main.star
@@ -55,6 +55,9 @@
         execution_timeout = 1 * time.hour,
         dimensions = {"cpu": "x86-64", "os": os, "pool": "luci.flex.%s" % bucket},
         triggered_by = triggered_by,
+        experiments = {
+            "luci.recipes.use_python3": 100,
+        },
     )
 
 luci.logdog(