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

src/arm/interface-descriptors-arm.cc

Index: src/arm/interface-descriptors-arm.cc
diff --git a/src/arm/interface-descriptors-arm.cc b/src/arm/interface-descriptors-arm.cc
index e54dd5c05914fe099007242c38ac7ef0662391a2..ddaf9e52136383e9d387c36abde3e5f831b87e7a 100644
--- a/src/arm/interface-descriptors-arm.cc
+++ b/src/arm/interface-descriptors-arm.cc
@@ -95,6 +95,10 @@ void ToNumberDescriptor::InitializePlatformSpecific(
 }
 
 
+// static
+const Register ToObjectDescriptor::ReceiverRegister() { return r0; }
+
+
 void NumberToStringDescriptor::InitializePlatformSpecific(
     CallInterfaceDescriptorData* data) {
   Register registers[] = {r0};