The webkit-codegen module represents a code generation tool, so the tests in
this module ensures the code generated by the tool is correct. We do this by
using two types of test-resource files: input and output files. The input files
live under codegen/ while the output files live under codegen-expected/.
Each test consists of parsing the input file, then passing that file to the tool
to perform some code transformation/generation, and finally validating the
output against one or several output file.
The input and output files are named in such a way that they correspond to how
the tool names its generated files, e.g. running boundary interface generation
for Foo.java will generate a file named FooBoundaryInterface.java.

The folder deps/android/webkit/ contains classes that should be seen as
android.webkit classes. These classes are special because they need special
treatment by the code generation tool (since the support library will never
reference those classes directly, but instead create its own versions of them).