Extract common code in string compare loops.

src/ia32/code-stubs-ia32.h

Index: src/ia32/code-stubs-ia32.h
diff --git a/src/ia32/code-stubs-ia32.h b/src/ia32/code-stubs-ia32.h
index a17ebdac5833f040f0c02af2c88b79153e6b08d1..649b98643873363d61c870828fbfe300accdca9b 100644
--- a/src/ia32/code-stubs-ia32.h
+++ b/src/ia32/code-stubs-ia32.h
@@ -391,10 +391,16 @@ class StringCompareStub: public CodeStub {
                                             Register scratch2);
 
  private:
-  Major MajorKey() { return StringCompare; }
-  int MinorKey() { return 0; }
+  virtual Major MajorKey() { return StringCompare; }
+  virtual int MinorKey() { return 0; }
+  virtual void Generate(MacroAssembler* masm);
 
-  void Generate(MacroAssembler* masm);
+  static void GenerateAsciiCharsCompareLoop(MacroAssembler* masm,
+                                            Register left,
+                                            Register right,
+                                            Register length,
+                                            Register scratch,
+                                            NearLabel* chars_not_equal);
 };