Change root visitor to use Object**.

Simplifies code and improves the performance of root visiting since
we usually don't need to check to see if the object moved.

Change-Id: Iba998f5a15ae1fa1b53ca5226dd2168a411196cf
diff --git a/runtime/stack.cc b/runtime/stack.cc
index fd7d981..864b86a 100644
--- a/runtime/stack.cc
+++ b/runtime/stack.cc
@@ -189,6 +189,11 @@
   }
 }
 
+uintptr_t* StackVisitor::GetGPRAddress(uint32_t reg) const {
+  DCHECK(cur_quick_frame_ != NULL) << "This is a quick frame routine";
+  return context_->GetGPRAddress(reg);
+}
+
 uintptr_t StackVisitor::GetGPR(uint32_t reg) const {
   DCHECK(cur_quick_frame_ != NULL) << "This is a quick frame routine";
   return context_->GetGPR(reg);