[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_x86.cc b/compiler/optimizing/code_generator_x86.cc
index 879216d..6ac4ad7 100644
--- a/compiler/optimizing/code_generator_x86.cc
+++ b/compiler/optimizing/code_generator_x86.cc
@@ -1120,6 +1120,14 @@
   UNUSED(constant);
 }
 
+void LocationsBuilderX86::VisitMemoryBarrier(HMemoryBarrier* memory_barrier) {
+  memory_barrier->SetLocations(nullptr);
+}
+
+void InstructionCodeGeneratorX86::VisitMemoryBarrier(HMemoryBarrier* memory_barrier) {
+  GenerateMemoryBarrier(memory_barrier->GetBarrierKind());
+}
+
 void LocationsBuilderX86::VisitReturnVoid(HReturnVoid* ret) {
   ret->SetLocations(nullptr);
 }