swarmbucket: allow overriding config

appengine/cr-buildbucket/proto/project_config.proto

 // Copyright 2015 The Swarming Authors. All rights reserved.
 // Use of this source code is governed by the Apache v2.0 license that can be
 // found in the LICENSE file.
 
 // Schemas for project configs.
 
 syntax = "proto2";
 
 package buildbucket;
 
@@ skipping 23 matching lines @@
     // Repository URL of the recipe package.
     optional string repository = 1;
     // Name of the recipe to run.
     optional string name = 2;
     // colon-separated build properties to set.
     // A property can be overriden by "properties" build parameter.
     //
     // Use this field for string properties and use properties_j for other
     // types.
     repeated string properties = 3;
-    // Same as properties, but the value must valid JSON or empty. For example
+    // Same as properties, but the value must valid JSON. For example
     //   properties_j: "a:1"
     // means property a is a number 1, not string "1".
     //
-    // If empty, it means no property must be defined. In particular, it removes
+    // If null, it means no property must be defined. In particular, it removes
     // a default value for the property, if any.
     //
     // Fields properties and properties_j can be used together, but cannot both
     // specify values for same property.
     repeated string properties_j = 4;
   }
 
+  // A builder has a name, a category and specifies what should happen if a
+  // build is scheduled to that builder.
+  //
+  // SECURITY WARNING: if adding more fields to this message, keep in mind that
+  // a user that has permissions to schedule a build to the bucket, can override
+  // this config.
   message Builder {
     // Name of the builder. Will be propagated to "builder" build tag and
     // "buildername" recipe property.
     optional string name = 1;
     // Builder category. Will be used for visual grouping, for example in Code Review.
     optional string category = 6;
     // Will be become to swarming task tags.
     // Each tag will end up in "swarming_tag" buildbucket tag, for example
     // "swarming_tag:builder:release"
     repeated string swarming_tags = 2;
@@ skipping 60 matching lines @@
   repeated Acl acls = 2;
   // Buildbucket-swarming integration.
   optional Swarming swarming = 3;
 }
 
 // Schema of buildbucket.cfg file, a project config.
 message BuildbucketCfg {
   // All buckets defined for this project.
   repeated Bucket buckets = 1;
 }