feat(screenshot): Update screenshot golds for merged PR (#3365)

Author: tinayuangao

tools/gulp/tasks/screenshots.ts

@@ -21,11 +21,17 @@ task('screenshots', () => {
       .then((files: any[]) => downloadAllGoldsAndCompare(files, database, prNumber))
       .then((results: boolean) => updateResult(database, prNumber, results))
       .then((result: boolean) => updateGithubStatus(result, prNumber))
-      .then(() => uploadScreenshots(prNumber, 'diff'))
-      .then(() => uploadScreenshots(prNumber, 'test'))
+      .then(() => uploadScreenshots('diff', prNumber))
+      .then(() => uploadScreenshots('test', prNumber))
       .then(() => updateTravis(database, prNumber))
       .then(() => setScreenFilenames(database, prNumber))
       .then(() => database.goOffline(), () => database.goOffline());
+  } else if (process.env['TRAVIS']) {
+    // Only update golds and filenames for build
+    let database = openFirebaseScreenshotsDatabase();
+    uploadScreenshots('gold')
+      .then(() => setScreenFilenames(database))
+      .then(() => database.goOffline(), () => database.goOffline());
   }
 });
 
@@ -70,19 +76,19 @@ function getLocalScreenshotFiles(dir: string): string[] {
  * Upload screenshots to google cloud storage.
  * @param prNumber - The key used in firebase. Here it is the PR number.
  *   If there's no prNumber, we will upload images to 'golds/' folder
- * @param mode - Can be 'test' or 'diff' or null.
+ * @param mode - Can be 'test' or 'diff' or 'gold'.
  *   If the images are the test results, mode should be 'test'.
  *   If the images are the diff images generated, mode should be 'diff'.
- *   For golds mode should be null.
+ *   For golds mode should be 'gold'.
  */
-function uploadScreenshots(prNumber?: string, mode?: 'test' | 'diff') {
+function uploadScreenshots(mode?: 'test' | 'diff' | 'gold', prNumber?: string) {
   let bucket = openScreenshotsBucket();
 
   let promises: any[] = [];
   let localDir = mode == 'diff' ? path.join(SCREENSHOT_DIR, 'diff') : SCREENSHOT_DIR;
   getLocalScreenshotFiles(localDir).forEach((file: string) => {
     let fileName = path.join(localDir, file);
-    let destination = (mode == null || !prNumber) ?
+    let destination = (mode == 'gold' || !prNumber) ?
       `golds/${file}` : `screenshots/${prNumber}/${mode}/${file}`;
     promises.push(bucket.upload(fileName, { destination: destination }));
   });