Java in Chromium follows the Android Open Source style guide with the following exceptions/modifications:

"Top level directories" are defined as directories with a gyp file, such as base/ and content/, Chromium java should live in a directory named <top level directory>/android/java, with a package name org.chromium.<top level directory>.  Each top level directory's java should build into a distinct jar that honors the abstraction specified in a native checkdeps (e.g. org.chromium.base does not import org.chromium.content).  The full path of any java file should contain the complete package name.

For example, top level directory base/ might contain a file named base/android/java/org/chromium/base/Class.java.  This would get compiled into a chromium_base.jar (final jar name TBD).