3 files changed, 21 insertions, 0 deletions
diff --git a/net/http/http_request_headers.cc b/net/http/http_request_headers.cc
index fc2ebcd..93ead01 100644
--- a/net/http/http_request_headers.cc
+++ b/net/http/http_request_headers.cc
@@ -76,6 +76,13 @@ void HttpRequestHeaders::Clear() {
   headers_.clear();
 }
 
+void HttpRequestHeaders::SetHeaderIfMissing(const base::StringPiece& key,
+                                            const base::StringPiece& value) {
+  HeaderVector::iterator it = FindHeader(key);
+  if (it == headers_.end())
+    headers_.push_back(HeaderKeyValuePair(key.as_string(), value.as_string()));
+}
+
 void HttpRequestHeaders::SetHeader(const base::StringPiece& key,
                                    const base::StringPiece& value) {
   HeaderVector::iterator it = FindHeader(key);
diff --git a/net/http/http_request_headers.h b/net/http/http_request_headers.h
index 734194a..2962ae2 100644
--- a/net/http/http_request_headers.h
+++ b/net/http/http_request_headers.h
@@ -95,6 +95,12 @@ class HttpRequestHeaders {
   // in the vector remains the same.  When comparing |key|, case is ignored.
   void SetHeader(const base::StringPiece& key, const base::StringPiece& value);
 
+  // Sets the header value pair for |key| and |value|, if |key| does not exist.
+  // If |key| already exists, the call is a no-op.
+  // When comparing |key|, case is ignored.
+  void SetHeaderIfMissing(const base::StringPiece& key,
+                          const base::StringPiece& value);
+
   // Removes the first header that matches (case insensitive) |key|.
   void RemoveHeader(const base::StringPiece& key);
 
diff --git a/net/http/http_request_headers_unittest.cc b/net/http/http_request_headers_unittest.cc
index f3abfbe2..384ceeb 100644
--- a/net/http/http_request_headers_unittest.cc
+++ b/net/http/http_request_headers_unittest.cc
@@ -67,6 +67,14 @@ TEST(HttpRequestHeaders, SetEmptyHeader) {
   EXPECT_EQ("Foo: Bar\r\nBar:\r\n\r\n", headers.ToString());
 }
 
+TEST(HttpRequestHeaders, SetHeaderIfMissing) {
+  HttpRequestHeaders headers;
+  headers.SetHeaderIfMissing("Foo", "Bar");
+  EXPECT_EQ("Foo: Bar\r\n\r\n", headers.ToString());
+  headers.SetHeaderIfMissing("Foo", "Baz");
+  EXPECT_EQ("Foo: Bar\r\n\r\n", headers.ToString());
+}
+
 TEST(HttpRequestHeaders, RemoveHeader) {
   HttpRequestHeaders headers;
   headers.SetHeader("Foo", "bar");