Switch to UniquePtr.

Only one use of scoped_ptr was incorrect (but then again, I spent an afternoon
with valgrind finding and fixing them just last week).

Change-Id: If5ec1c8aa0794a4f652bfd1c0fffccf95facdc40
diff --git a/src/calling_convention_x86.cc b/src/calling_convention_x86.cc
index 148eee2..7257ef6 100644
--- a/src/calling_convention_x86.cc
+++ b/src/calling_convention_x86.cc
@@ -71,11 +71,9 @@
   return 0;
 }
 
-std::vector<ManagedRegister>* JniCallingConvention::ComputeRegsToSpillPreCall()
-{
+void JniCallingConvention::ComputeRegsToSpillPreCall(std::vector<ManagedRegister>& regs) {
   // No live values in registers (everything is on the stack) so never anything
   // to preserve.
-  return  new std::vector<ManagedRegister>();
 }
 
 bool JniCallingConvention::IsOutArgRegister(ManagedRegister) {