[stubs] Unify (and optimize) implementation of ToObject.

src/x87/interface-descriptors-x87.cc

Index: src/x87/interface-descriptors-x87.cc
diff --git a/src/x87/interface-descriptors-x87.cc b/src/x87/interface-descriptors-x87.cc
index dacbf1061d29b3f69ce5dc90c197491b60b6d645..7e03fac070ac1ee1aa6ca7a00cb8146b03bdb41f 100644
--- a/src/x87/interface-descriptors-x87.cc
+++ b/src/x87/interface-descriptors-x87.cc
@@ -103,6 +103,10 @@ void ToNumberDescriptor::InitializePlatformSpecific(
 }
 
 
+// static
+const Register ToObjectDescriptor::ReceiverRegister() { return eax; }
+
+
 void NumberToStringDescriptor::InitializePlatformSpecific(
     CallInterfaceDescriptorData* data) {
   Register registers[] = {eax};