Add support for Baker read barriers in UnsafeCASObject intrinsics.

Prior to doing the compare-and-swap operation, ensure the
expected reference stored in the holding object's field is
in the to-space by loading it, emitting a read barrier and
updating that field with a strong compare-and-set operation
with relaxed memory synchronization ordering (if needed).

Test: ART host and target tests and Nexus 5X boot test with Baker read barriers.
Bug: 29516905
Bug: 12687968
Change-Id: I480f6a9b59547f11d0a04777406b9bfeb905bfd2
diff --git a/runtime/interpreter/unstarted_runtime.cc b/runtime/interpreter/unstarted_runtime.cc
index 5a62bd7..cc88d7e 100644
--- a/runtime/interpreter/unstarted_runtime.cc
+++ b/runtime/interpreter/unstarted_runtime.cc
@@ -1271,7 +1271,7 @@
     mirror::HeapReference<mirror::Object>* field_addr =
         reinterpret_cast<mirror::HeapReference<mirror::Object>*>(
             reinterpret_cast<uint8_t*>(obj) + static_cast<size_t>(offset));
-    ReadBarrier::Barrier<mirror::Object, kWithReadBarrier, /*kAlwaysUpdateField*/true>(
+    ReadBarrier::Barrier<mirror::Object, kWithReadBarrier, /* kAlwaysUpdateField */ true>(
         obj,
         MemberOffset(offset),
         field_addr);
diff --git a/runtime/native/sun_misc_Unsafe.cc b/runtime/native/sun_misc_Unsafe.cc
index cdf4b14..644df07 100644
--- a/runtime/native/sun_misc_Unsafe.cc
+++ b/runtime/native/sun_misc_Unsafe.cc
@@ -65,7 +65,7 @@
     mirror::HeapReference<mirror::Object>* field_addr =
         reinterpret_cast<mirror::HeapReference<mirror::Object>*>(
             reinterpret_cast<uint8_t*>(obj.Ptr()) + static_cast<size_t>(offset));
-    ReadBarrier::Barrier<mirror::Object, kWithReadBarrier, /*kAlwaysUpdateField*/true>(
+    ReadBarrier::Barrier<mirror::Object, kWithReadBarrier, /* kAlwaysUpdateField */ true>(
         obj.Ptr(),
         MemberOffset(offset),
         field_addr);
diff --git a/runtime/read_barrier-inl.h b/runtime/read_barrier-inl.h
index 67e5a81..be95600 100644
--- a/runtime/read_barrier-inl.h
+++ b/runtime/read_barrier-inl.h
@@ -54,7 +54,7 @@
         // Slow-path.
         ref = reinterpret_cast<MirrorType*>(Mark(ref));
         // If kAlwaysUpdateField is true, update the field atomically. This may fail if mutator
-        // updates before us, but it's ok.
+        // updates before us, but it's OK.
         if (kAlwaysUpdateField && ref != old_ref) {
           obj->CasFieldStrongRelaxedObjectWithoutWriteBarrier<false, false>(
               offset, old_ref, ref);