X87: [stubs] Refactor StringCompareStub and use it for HStringCompareAndBranch.

src/x87/interface-descriptors-x87.cc

Index: src/x87/interface-descriptors-x87.cc
diff --git a/src/x87/interface-descriptors-x87.cc b/src/x87/interface-descriptors-x87.cc
index fc5b4be2f7239198fe2d12e06baefac6825261cb..c6e04dce849b28e274dade6674a6c5d6fa22034c 100644
--- a/src/x87/interface-descriptors-x87.cc
+++ b/src/x87/interface-descriptors-x87.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; }