[stubs] Refactor StringCompareStub and use it for HStringCompareAndBranch.

src/ia32/interface-descriptors-ia32.cc

Index: src/ia32/interface-descriptors-ia32.cc
diff --git a/src/ia32/interface-descriptors-ia32.cc b/src/ia32/interface-descriptors-ia32.cc
index 0fea67b76f6ae4f2e2e1519dc827f44f338b89fb..9ced41000b3179d32abcedfbdc011c92327ad04f 100644
--- a/src/ia32/interface-descriptors-ia32.cc
+++ b/src/ia32/interface-descriptors-ia32.cc
@@ -57,6 +57,10 @@ const Register InstanceOfDescriptor::LeftRegister() { return edx; }
 const Register InstanceOfDescriptor::RightRegister() { return eax; }
 
 
+const Register StringCompareDescriptor::LeftRegister() { return edx; }
+const Register StringCompareDescriptor::RightRegister() { return eax; }
+
+
 const Register ArgumentsAccessReadDescriptor::index() { return edx; }
 const Register ArgumentsAccessReadDescriptor::parameter_count() { return eax; }