Hydrogenize (and share) part of StoreTransition handler as a StoreTransitionStub.

src/mips64/interface-descriptors-mips64.cc

Index: src/mips64/interface-descriptors-mips64.cc
diff --git a/src/mips64/interface-descriptors-mips64.cc b/src/mips64/interface-descriptors-mips64.cc
index 06db80883124ff26cb5ca164650f7a6c67296293..a14a08bdbdb780fc1cdae15055112b3899bd1d54 100644
--- a/src/mips64/interface-descriptors-mips64.cc
+++ b/src/mips64/interface-descriptors-mips64.cc
@@ -29,7 +29,7 @@ const Register StoreDescriptor::NameRegister() { return a2; }
 const Register StoreDescriptor::ValueRegister() { return a0; }
 
 
-const Register ExtendStorageDescriptor::MapRegister() { return a3; }
+const Register StoreTransitionDescriptor::MapRegister() { return a3; }
 
 
 const Register ElementTransitionAndStoreDescriptor::MapRegister() { return a3; }