[stubs] Refactor StringCompareStub and use it for HStringCompareAndBranch.

src/code-factory.cc

Index: src/code-factory.cc
diff --git a/src/code-factory.cc b/src/code-factory.cc
index 63dba9d422ad609caa117c318a80ab4738479236..0d6b36b9d285d9b6277fae7b3db0a43609ed8ac2 100644
--- a/src/code-factory.cc
+++ b/src/code-factory.cc
@@ -198,6 +198,13 @@ Callable CodeFactory::StringAdd(Isolate* isolate, StringAddFlags flags,
 
 
 // static
+Callable CodeFactory::StringCompare(Isolate* isolate) {
+  StringCompareStub stub(isolate);
+  return Callable(stub.GetCode(), stub.GetCallInterfaceDescriptor());
+}
+
+
+// static
 Callable CodeFactory::Typeof(Isolate* isolate) {
   TypeofStub stub(isolate);
   return Callable(stub.GetCode(), stub.GetCallInterfaceDescriptor());