Handle variable size of methods properly between 32 and 64 bit.

Bug: 19100762
Change-Id: I62358905fa882284d0201ed3c1e97e1286ccec5f
diff --git a/runtime/stack.cc b/runtime/stack.cc
index b771aa7..b39aebf 100644
--- a/runtime/stack.cc
+++ b/runtime/stack.cc
@@ -134,7 +134,8 @@
     } else {
       return cur_shadow_frame_->GetVRegReference(0);
     }
-  } else if (m->IsOptimized(sizeof(void*))) {
+  } else if (m->IsOptimized(GetInstructionSetPointerSize(
+      Runtime::Current()->GetInstructionSet()))) {
     // TODO: Implement, currently only used for exceptions when jdwp is enabled.
     UNIMPLEMENTED(WARNING)
         << "StackVisitor::GetThisObject is unimplemented with the optimizing compiler";