HttpRequestHeaders refactor.

base/string_util.h

Index: base/string_util.h
diff --git a/base/string_util.h b/base/string_util.h
index 586c60ccbe6703049734164a1d7c283becb4a849..28cd26fc2d5d9fd1ec43ea4948be749cc728e2a0 100644
--- a/base/string_util.h
+++ b/base/string_util.h
@@ -575,6 +575,14 @@ void SplitStringDontTrim(const std::string& str,
                          char s,
                          std::vector<std::string>* r);
 
+// The same as SplitString, but use a substring delimiter instead of a char.
+void SplitStringUsingSubstr(const string16& str,
+                            const string16& s,
+                            std::vector<string16>* r);
+void SplitStringUsingSubstr(const std::string& str,
+                            const std::string& s,
+                            std::vector<std::string>* r);
+
 // Splits a string into its fields delimited by any of the characters in
 // |delimiters|.  Each field is added to the |tokens| vector.  Returns the
 // number of tokens found.