build: cancel screenshot diff if there is no activity

* No longer just gives the screenshot diff task 8 minutes to pass, because the run time can vary. Now it just exits the process if the last action in the task takes longer than 6 minutes.
* Instead of just closing the firebase connection, the process will be exited with an error code. Just closing the connection is not helpful and breaks the screenshot diff Web Interface.

Author: devversion

tools/gulp/tasks/screenshots.ts

@@ -34,6 +34,9 @@ const FIREBASE_IMAGE = `${TEMP_FOLDER}/screenshot/images`;
 const FIREBASE_DATA_GOLDENS = `screenshot/goldens`;
 const FIREBASE_STORAGE_GOLDENS = 'goldens';
 
+const lastActionTimeout = 1000 * 60 * 6;
+const lastActionRefreshInterval = 1000 * 45;
+
 /** Task which upload screenshots generated from e2e test. */
 task('screenshots', () => {
   const prNumber = process.env['TRAVIS_PULL_REQUEST'];
@@ -45,13 +48,18 @@ task('screenshots', () => {
     const firebaseApp = connectFirebaseScreenshots();
     const database = firebaseApp.database();
 
+    let lastActionTime = Date.now();
+
     // If this task hasn't completed in 8 minutes, close the firebase connection.
-    const timeoutId = setTimeout(() => {
-      console.error('Screenshot tests did not finish in 8 minutes, closing Firebase connection.');
-      return firebaseApp.delete();
-    }, 60 * 1000 * 8);
+    const timeoutId = setInterval(() => {
+      if (lastActionTime + lastActionTimeout <= Date.now()) {
+        clearTimeout(timeoutId);
+        console.error('Last action for screenshot tests did not finish in ' +
+            (lastActionTime / 1000 / 60) + ' minutes. Closing Firebase connection...');
+        return firebaseApp.delete().then(() => process.exit(1));
+      }
+    }, lastActionRefreshInterval);
 
-    let lastActionTime = Date.now();
     return uploadTravisJobInfo(database, prNumber)
       .then(() => {
         console.log(`  Downloading screenshot golds from Firebase...`);