Do not override User-Agent header added by WebCore

net/http/http_request_headers_unittest.cc

 // Copyright (c) 2010 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "net/http/http_request_headers.h"
 
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace net {
 
@@ skipping 49 matching lines @@
   EXPECT_EQ("FooBar: smokes\r\nFoo: crack\r\n\r\n", headers_ref.ToString());
 }
 
 TEST(HttpRequestHeaders, SetEmptyHeader) {
   HttpRequestHeaders headers;
   headers.SetHeader("Foo", "Bar");
   headers.SetHeader("Bar", "");
   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");
   headers.RemoveHeader("Foo");
   EXPECT_EQ("\r\n", headers.ToString());
 }
 
 TEST(HttpRequestHeaders, RemoveHeaderMissingHeader) {
   HttpRequestHeaders headers;
   headers.SetHeader("Foo", "bar");
@@ skipping 71 matching lines @@
   HttpRequestHeaders headers2;
   headers2.SetHeader("B", "b");
   headers2.SetHeader("C", "c");
   headers.CopyFrom(headers2);
   EXPECT_EQ("B: b\r\nC: c\r\n\r\n", headers.ToString());
 }
 
 }  // namespace
 
 }  // namespace net