Want to contribute? Great! First, read this page (including the small print at the end).
Pull requests can be hard to review if they try to tackle too many things at once. Phabricator's “Writing Reviewable Code” provides a set of guidelines that help increase the likelihood of your pull request getting merged.
In short (slightly modified from the original article):
Before we can use your code, you must sign the Google Individual Contributor License Agreement (CLA), which you can do online. The CLA is necessary mainly because you own the copyright to your changes, even after your contribution becomes part of our codebase, so we need your permission to use and distribute your code. We also need to be sure of various other things—for instance that you‘ll tell us if you know that your code infringes on other people’s patents. You don‘t have to sign the CLA until after you’ve submitted your code for review and a member has approved it, but you must do it before we can put your code into our codebase. Before you start working on a larger contribution, you should get in touch with us first through the issue tracker with your idea so that we can help out and possibly guide you. Coordinating up front makes it much easier to avoid frustration later on.
All submissions, including submissions by project members, require review. We allow pull requests to be filed, but we perform code reviews on codereview.cc.
Contributions made by corporations are covered by a different agreement than the one above, the Software Grant and Corporate Contributor License Agreement.