[optimizing] Add memory barriers in constructors when needed

If a class has final fields we must add a memory barrier before
returning from constructor. This makes sure the fields are visible to
other threads.

Bug: 19851497
Change-Id: If8c485092fc512efb9636cd568cb0543fb27688e
diff --git a/compiler/optimizing/code_generator_arm64.cc b/compiler/optimizing/code_generator_arm64.cc
index efc41e7..779340d 100644
--- a/compiler/optimizing/code_generator_arm64.cc
+++ b/compiler/optimizing/code_generator_arm64.cc
@@ -2430,6 +2430,14 @@
   }
 }
 
+void LocationsBuilderARM64::VisitMemoryBarrier(HMemoryBarrier* memory_barrier) {
+  memory_barrier->SetLocations(nullptr);
+}
+
+void InstructionCodeGeneratorARM64::VisitMemoryBarrier(HMemoryBarrier* memory_barrier) {
+  GenerateMemoryBarrier(memory_barrier->GetBarrierKind());
+}
+
 void LocationsBuilderARM64::VisitReturn(HReturn* instruction) {
   LocationSummary* locations = new (GetGraph()->GetArena()) LocationSummary(instruction);
   Primitive::Type return_type = instruction->InputAt(0)->GetType();