[stubs] Refactor StringCompareStub and use it for HStringCompareAndBranch.

src/interface-descriptors.cc

Index: src/interface-descriptors.cc
diff --git a/src/interface-descriptors.cc b/src/interface-descriptors.cc
index b66f67c1d13f267fc716e7b06fcd549b1e782e2f..b446d6396af50450d163021798e87b88d5f1fdc0 100644
--- a/src/interface-descriptors.cc
+++ b/src/interface-descriptors.cc
@@ -167,6 +167,13 @@ void InstanceOfDescriptor::InitializePlatformSpecific(
 }
 
 
+void StringCompareDescriptor::InitializePlatformSpecific(
+    CallInterfaceDescriptorData* data) {
+  Register registers[] = {LeftRegister(), RightRegister()};
+  data->InitializePlatformSpecific(arraysize(registers), registers);
+}
+
+
 void ToStringDescriptor::InitializePlatformSpecific(
     CallInterfaceDescriptorData* data) {
   Register registers[] = {ReceiverRegister()};