Eventually you’ll have your build setup, and want to get to work. In a perfect world, we would have all the time we needed to read every line of code and understand it before writing our first line of code. In practice, we’d have a hard time reading just the checkins that happen in one day if we did nothing else, so none of us will ever be able to read all of the code. So, what can we do? We suggest you develop your own plan for learning what you need, here are some suggested starting points.
Fortunately for us, Chromium has some top quality design docs here. While these can go a bit stale (for instance, when following along, you may find references to files that have been moved or renamed or refactored out of existence), it is awesome to be able to comprehend the way that the code fits together overall.
Read the most important dev docs
See if your group has any startup docs
There may be some docs that people working on the same code will care about while others don’t need to know as much detail.
Learn some of the code idioms:
Later, as time permits, skim all the design docs, reading where it seems relevant.
Get good at using code search (or your code browsing tool of choice)
Learn who to ask how the code works hints here.
Debug into the code you need to learn, with a debugger if you can, log statements and grepping if you cannot.
Look at the differences in what you need to understand and you currently understand. For instance, if your group does a lot of GUI programming, then maybe you can invest time in learning GTK+, Win32, or Cocoa programming.