Move MarkObject to mark_sweep.cc

Maybe fixes mac build.

Change-Id: I7c018922be8e159001498d30682435643bed1dfd
diff --git a/runtime/gc/collector/mark_sweep.cc b/runtime/gc/collector/mark_sweep.cc
index 42bca84..d59a21d 100644
--- a/runtime/gc/collector/mark_sweep.cc
+++ b/runtime/gc/collector/mark_sweep.cc
@@ -337,6 +337,11 @@
   }
 }
 
+mirror::Object* MarkSweep::MarkObject(mirror::Object* obj) {
+  MarkObject(obj, nullptr, MemberOffset(0));
+  return obj;
+}
+
 inline void MarkSweep::MarkObjectNonNullParallel(mirror::Object* obj) {
   DCHECK(obj != nullptr);
   if (MarkObjectParallel(obj)) {
diff --git a/runtime/gc/collector/mark_sweep.h b/runtime/gc/collector/mark_sweep.h
index 1dac342..7692b06 100644
--- a/runtime/gc/collector/mark_sweep.h
+++ b/runtime/gc/collector/mark_sweep.h
@@ -188,10 +188,7 @@
   // Marks an object.
   virtual mirror::Object* MarkObject(mirror::Object* obj) OVERRIDE
       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_)
-      EXCLUSIVE_LOCKS_REQUIRED(Locks::heap_bitmap_lock_) {
-    MarkObject(obj, nullptr, MemberOffset(0));
-    return obj;
-  }
+      EXCLUSIVE_LOCKS_REQUIRED(Locks::heap_bitmap_lock_);
   void MarkObject(mirror::Object* obj, mirror::Object* holder, MemberOffset offset)
       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_)
       EXCLUSIVE_LOCKS_REQUIRED(Locks::heap_bitmap_lock_);