Change == into an instance call to allow polymorphic inlining of ==.

runtime/vm/locations.cc

Index: runtime/vm/locations.cc
===================================================================
--- runtime/vm/locations.cc	(revision 29353)
+++ runtime/vm/locations.cc	(working copy)
@@ -159,6 +159,8 @@
     f->Print("S%+" Pd "", stack_index());
   } else if (kind() == kDoubleStackSlot) {
     f->Print("DS%+" Pd "", stack_index());
+  } else if (kind() == kQuadStackSlot) {
+    f->Print("QS%+" Pd "", stack_index());
   } else {
     f->Print("%s", Name());
   }