Add compiling class to the DexCompilationUnit.

Use it to simplify HInstructionBuilder and reduce the
number of class resolution calls.

Test: m test-art-host-gtest
Test: testrunner.py --host --optimizing
Test: Pixel 2 XL boots.
Change-Id: Ib4f9b4ea61235841e653a03a40755a39c7de7504
6 files changed