Oat file checksums for boot image extensions.

Modify the oat checksums check for boot image extensions.
There may be more extensions loaded at runtime than when the
oat file was compiled, so we need to check the checksum type
from the checksums string to determine whether to use an
image checksum or dex file checksum. Different checksums
can be valid for the same boot class path.

The creation of boot image extensions and other aspects
of loading them shall be implemented in separate CLs.

Test: m test-art-host-gtest
Test: testrunner.py --host --optimizing
Test: aosp_taimen-userdebug boots.
Change-Id: I43d1f9464678784e902ad72f4a89cf38b4786122
7 files changed