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

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 070228ddd20d16422d36a8eec3139d0d3625c745..7e1496744bb1917f1f26eec4465bedaa1a0c2aa6 100644
--- a/src/mips/interface-descriptors-mips.cc
+++ b/src/mips/interface-descriptors-mips.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; }