Revert "Revert "CHA for abstract methods.""

This reverts commit 8ebc8bf055e8bd8f6f167e65a69cf4dae136db55.

When we set the single-implementation method for an abstract method, it
need to be protected by the cha-lock.

Test: new testcase and ART_TEST_JIT=true m -j20 test-art-host-run-test
Change-Id: I66acb20ffa7e49dd9c391f001e3bb52f961872e4
diff --git a/runtime/art_method.cc b/runtime/art_method.cc
index a3d9ba6..ec789f5 100644
--- a/runtime/art_method.cc
+++ b/runtime/art_method.cc
@@ -55,15 +55,13 @@
 extern "C" void art_quick_invoke_static_stub(ArtMethod*, uint32_t*, uint32_t, Thread*, JValue*,
                                              const char*);
 
-ArtMethod* ArtMethod::GetSingleImplementation() {
+ArtMethod* ArtMethod::GetSingleImplementation(PointerSize pointer_size) {
   DCHECK(!IsNative());
   if (!IsAbstract()) {
     // A non-abstract's single implementation is itself.
     return this;
   }
-  // TODO: add single-implementation logic for abstract method by storing it
-  // in ptr_sized_fields_.
-  return nullptr;
+  return reinterpret_cast<ArtMethod*>(GetDataPtrSize(pointer_size));
 }
 
 ArtMethod* ArtMethod::FromReflectedMethod(const ScopedObjectAccessAlreadyRunnable& soa,