ARM: Use ubfx and movw instructions to avoid a PC-relative load on

src/mark-compact.cc

Index: src/mark-compact.cc
===================================================================
--- src/mark-compact.cc	(revision 10578)
+++ src/mark-compact.cc	(working copy)
@@ -886,6 +886,15 @@
     heap->mark_compact_collector()->MarkObject(object, mark);
   }
 
+#ifdef V8_TARGET_ARCH_ARM
+  static inline void VisitEmbeddedMapSignature(Heap* heap, RelocInfo* rinfo) {
+    ASSERT(rinfo->rmode() == RelocInfo::MAP_SIGNATURE);
+    HeapObject* object = HeapObject::cast(rinfo->target_object());
+    MarkBit mark = Marking::MarkBitFrom(object);
+    heap->mark_compact_collector()->MarkObject(object, mark);
+  }
+#endif
+
   static inline void VisitCodeTarget(Heap* heap, RelocInfo* rinfo) {
     ASSERT(RelocInfo::IsCodeTarget(rinfo->rmode()));
     Code* target = Code::GetCodeFromTargetAddress(rinfo->target_address());