tools/android/loading Support "report" tasks in the Clovis frontend

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

 # Appengine Frontend for Clovis
 
 [TOC]
 
 ## Usage
 
 Visit the application URL in your browser, and upload a JSON dictionary with the
 following keys:
 
--   `action` (string): the action to perform. Only `trace` is supported.
+-   `action` (string): the action to perform. Only `trace` and `report` are
+    supported.
 -   `action_params` (dictionary): the parameters associated to the action.
     See below for more details.
 -   `backend_params` (dictionary): the parameters configuring the backend for
     this task. See below for more details.
 
 ### Parameters for `backend_params`
 
 -   `instance_count` (int): Number of Compute Engine instances that will be
     started for this task.
 -   `storage_bucket` (string): Name of the storage bucket used by the backend
     instances. Backend code and data must have been previously deployed to this
     bucket using the `deploy.sh` [script][4].
 -   `tag` (string, optional): tag internally used to associate tasks to backend
     ComputeEngine instances. This parameter should not be set in general, as it
     is mostly exposed for development purposes. If this parameter is not
     specified, a unique tag will be generated.
 -   `timeout_hours` (int, optional): if workers are still alive after this
     delay, they will be forcibly killed, to avoid wasting Compute Engine
     resources. Defaults to `5`.
 
 ### Parameters for the `trace` action
 
+The trace action takes a list of URLs as input and generates a list of traces by
+running Chrome.
+
 -   `urls` (list of strings): the list of URLs to process.
 -   `repeat_count` (integer, optional): the number of traces to be generated
     for each URL. Defaults to 1.
 -   `emulate_device` (string, optional): the device to emulate (e.g. `Nexus 4`).
 -   `emulate_network` (string, optional): the network to emulate.
 
+### Parameters for the `report` action
+
+Finds all the traces in the bucket (specified in the backend parameters) and
+generates a report in BigQuery.
+
+This action has no parameters.
+
 ## Development
 
 ### Design overview
 
 -   Appengine configuration:
     -   `app.yaml` defines the handlers. There is a static handler for all URLs
     in the `static/` directory, and all other URLs are handled by the
     `clovis_frontend.py` script.
     -   `queue.yaml` defines the task queues associated with the application. In
         particular, the `clovis-queue` is a pull-queue where tasks are added by
@@ skipping 49 matching lines @@
 # Install dependencies in the lib/ directory.
 pip install -r requirements.txt -t lib
 # Deploy.
 gcloud preview app deploy app.yaml
 ```
 
 [1]: https://cloud.google.com/sdk
 [2]: https://cloud.google.com/appengine/docs/python/taskqueue
 [3]: https://cloud.google.com/appengine/docs/python/config/queue
 [4]: ../backend/README.md#Deploy-the-code