message: Add build options for differential serving.
  browserCapabilities and basePath.
diff: @@ -99,6 +99,34 @@ export interface ProjectBuildOptions {
  /** Use babel to compile all ES6 JS down to ES5 for older browsers. */
  compile?: boolean
  };
  +
  + /**
  + * Capabilities required for a browser to consume this build. Values include
  + * `es2015` and `push`. See canonical list at:
  + * https://github.com/Polymer/prpl-server-node/blob/master/src/capabilities.ts
  + *
  + * This field is purely a hint to servers reading this configuration, and
  + * does not affect the build process. A server supporting differential
  + * serving (e.g. prpl-server) can use this field to help decide which build
  + * to serve to a given user agent.
  + */
  + browserCapabilities?: string[];
  +
  + /**
  + * Apply transformations during build to support serving this build from a
  + * non-root path, such as when doing differential serving based on user
  + * agent. This works well in conjunction with the convention of using
  + * relative URLs for static resources and absolute URLs for application
  + * routes.
  + *
  + * - Find and update the entrypoint's `<base>` tag.
  + * - Prefix Service Worker pre-cached resources.
  + * - Prefix Push Manifest resources.
  + *
  + * If `true`, use the build `name`. If a `string`, use that value.
  + * Leading/trailing slashes are optional.
  + */
  + basePath?: boolean | string;
  }
  export const buildPresets = new Map<string, ProjectBuildOptions>([
  