Update rietveld references in catapult docs to Gerrit.

CONTRIBUTING.md

 <!-- Copyright 2015 The Chromium Authors. All rights reserved.
      Use of this source code is governed by a BSD-style license that can be
      found in the LICENSE file.
 -->
 # Code of Conduct
 
 We follow the [Chromium code of conduct](
 https://chromium.googlesource.com/chromium/src/+/master/CODE_OF_CONDUCT.md) in
 our our repos and organizations, mailing lists, and other communications.
 
@@ skipping 10 matching lines @@
 
 ```
 cd catapult
 git checkout -t -b foo origin/master
 ... edit files ...
 git commit -a -m "New files"
 ```
 
 Once you're ready for a review do:
 
-`git cl upload --rietveld`
+`git cl upload`
 
-Once uploaded you can view the CL in Rietveld and **request a review** by
-clicking the 'publish & mail' link, and adding a reviewer from the
-[OWNERS](/OWNERS) file. You can also click the "CQ Dry Run" link to run all
+Once uploaded you can view the CL in Gerrit and **request a review** by
+clicking the "Add reviewer" link, and adding a reviewer from the
+[OWNERS](/OWNERS) file. You can also click the "CQ Dry Run" button to run all
 the tests on your change.
 
 If you get review feedback, edit and commit locally and then do another upload
 with the new files. Before you commit you'll want to sync to the tip-of-tree.
 You can either merge or rebase, it's up to you.
 
 Then, submit your changes through the commit queue by checking the "Commit" box.
 
 Once everything is landed, you can cleanup your branch.
 
@@ skipping 51 matching lines @@
    * [perf dashboard](/dashboard/README.md)
    * [systrace](/systrace/README.md)
    * [telemetry](/telemetry/README.md)
    * [trace-viewer](/tracing/README.md)
 
 # Tests
 
 Check individual project documentation for instructions on how to run tests.
 You can also check the current status of our tests on the
 [waterfall](http://build.chromium.org/p/client.catapult/waterfall).
-Use the "commit" checkbox in rietveld to commit through the commit queue, which
-automatically runs all tests. Run the tests before committing with the
-"CQ dry run" link.
+Use the "Submit to CQ" button in Gerrit to commit through the commit queue,
+which automatically runs all tests. Run the tests before committing with the
+"CQ Dry Run" button.
 
 # Updating Chromium's about:tracing (rolling DEPS)
 
 Chromium's DEPS file needs to be rolled to the catapult revision containing your
 change in order for it to appear in Chrome's about:tracing or other
 third_party/catapult files. Follow the [directions for rolling DEPS](/docs/rolling-deps.md)
 to do this.
 
 # Adding a new project
 
 Please read the [directory structure guide](/docs/directory-structure.md)
 to learn the conventions for new directories.