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

src/mips/interface-descriptors-mips.cc

Index: src/mips/interface-descriptors-mips.cc
diff --git a/src/mips/interface-descriptors-mips.cc b/src/mips/interface-descriptors-mips.cc
index f0618ad98109626bddfa051a176ae8a27412998a..df3652052fa43c8ff01abfbe30cc143e1fb7f641 100644
--- a/src/mips/interface-descriptors-mips.cc
+++ b/src/mips/interface-descriptors-mips.cc
@@ -95,6 +95,10 @@ void ToNumberDescriptor::InitializePlatformSpecific(
 }
 
 
+// static
+const Register ToObjectDescriptor::ReceiverRegister() { return a0; }
+
+
 void NumberToStringDescriptor::InitializePlatformSpecific(
     CallInterfaceDescriptorData* data) {
   Register registers[] = {a0};