Change ClassExt.originalDexFile field to an opaque Object

We are changing this field to be either a DexCache object
or a byte[] in order to ensure we will not have multiple 
copies of the dexfile bytes held in memory.

Bug: 31455788
Test: ./art/test/testrunner/testrunner.py --host -j40
Change-Id: Ifdb19cb516311aba37b7f5e5aeab0dc1ecbcb758
1 file changed