tools/android/loading Loading trace database improvements

tools/android/loading/cloud/backend/README.md

 # Clovis in the Cloud: Developer Guide
 
 This document describes how to collect Chromium traces using Google Compute
 Engine.
 
 [TOC]
 
 ## Initial setup
 
 Install the [gcloud command line tool][1].
@@ skipping 92 matching lines @@
 # CLOUD_STORAGE_PATH is the path in Google Storage where generated traces will
 # be stored.
 # CHROME_PATH is the path to the Chrome executable on the host.
 # CHROMIUM_SRC is the Chromium src directory.
 cat >$CONFIG_FILE << EOF
 {
   "project_name" : "$PROJECT_NAME",
   "cloud_storage_path" : "$CLOUD_STORAGE_PATH",
   "chrome_path" : "$CHROME_PATH",
   "src_path" : "$CHROMIUM_SRC",
-  "taskqueue_tag" : "some_tag"
+  "taskqueue_tag" : "some_tag",
+  "trace_database_filename" : "trace_database.json"  # Optional
 }
 EOF
 ```
 
 Launch the app, passing the path to the deployment configuration file:
 
 ```shell
 python $CHROMIUM_SRC/tools/android/loading/cloud/backend/worker.py \
     --config $CONFIG_FILE
 ```
 
 You can now [use the app][2].
 
 Tear down the local environment:
 
 ```shell
 deactivate
 ```
 
 [1]: https://cloud.google.com/sdk
 [2]: #Use-the-app
 [3]: ../frontend/README.md