Add support for processing class loader contexts

Initial support for recognizing the class loader contexts.

In order to correctly compile dex files which at runtime are loaded with
a non-trivial class loader chain we need to make dex2oat aware of the
precise runtime context.

This CL adds the infrastructure to process arbitrary and arbitrary chain
of class loaders. ClassLoaderContext is able to parse a class loader
spec from a string and create the runtime structure based on it.

The integration with dex2oat and oat file assistant will follow up.

The string specification looks like
"PCL[lib1.dex:lib2.dex];DLC[lib3.dex]"

It describes how the class loader chain should be build in order to
ensure classes are resolved during dex2aot as they would be resolved at
runtime. This spec will be encoded in the oat file. If at runtime the
dex file will be loaded in a different context, the oat file will be
rejected.

The chain is interpreted in the natural 'parent order', meaning that
class loader 'i+1' will be the parent of class loader 'i'. The
compilation sources will be added to the classpath of the last class
loader. This allows the compiled dex files to be loaded at runtime in a
class loader that contains other dex files as well (e.g. shared
libraries).

Note that we accept chains for which the source dex files specified
with --dex-file are found in the classpath. In this case the source dex
files will be removed from the any class loader's classpath possibly
resulting in empty class loaders.

* This is the first CL, which adds the infrastructure for processing
a class loader context. Currently it CHECKS that only a single
PathClassLoader is created.

Test: m test-art-host
Bug: 38138251
Change-Id: I312aa12b5732288f3c1df4746b5775a32e0bfb04

0 files changed, 0 insertions, 0 deletions