message: added onBeforePrint in bundler
diff: @@ -90,7 +90,7 @@ export class Bundler {
  return this.getDependencyPaths({ entries: this.outputCSS, themeEntries: {} });
  }
  - public generateCSS(usedSheetPaths?:string[]):string {
  + public generateCSS(usedSheetPaths?: string[], onBeforePrint?: (meta: StylableMeta) => void): string {
  // collect stylesheet meta list
  let outputMetaList: StylableMeta[];
  let themeEntries: ThemeEntries = this.themeAcc;
  @@ -120,10 +120,14 @@ export class Bundler {
  // emit output CSS
  return outputMetaList.reverse()
  - .map(meta => meta.outputAst!.toString())
  + .map(meta => {
  + onBeforePrint && onBeforePrint(meta);
  + return meta.outputAst!.toString()
  + })
  .filter(entryCSS => !!entryCSS)
  .join('\n');
  }
  +
  private cleanUnused(meta: StylableMeta, usedPaths: string[]): void {
  meta.imports.forEach(importRequest => removeUnusedRules(meta.outputAst!, meta, importRequest, usedPaths, this.resolvePath.bind(this)));
  }
  