Do not override User-Agent header added by WebCore

net/url_request/url_request_http_job.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/url_request/url_request_http_job.h"
 
 #include "base/base_switches.h"
 #include "base/command_line.h"
 #include "base/compiler_specific.h"
 #include "base/file_util.h"
@@ skipping 176 matching lines @@
   // Ensure that we do not send username and password fields in the referrer.
   GURL referrer(request_->GetSanitizedReferrer());
 
   request_info_.url = request_->url();
   request_info_.referrer = referrer;
   request_info_.method = request_->method();
   request_info_.load_flags = request_->load_flags();
   request_info_.priority = request_->priority();
 
   if (request_->context()) {
-    request_info_.extra_headers.SetHeader(
+    request_info_.extra_headers.SetHeaderIfMissing(
         HttpRequestHeaders::kUserAgent,
         request_->context()->GetUserAgent(request_->url()));
   }
 
   AddExtraHeaders();
   AddCookieHeaderAndStart();
 }
 
 void URLRequestHttpJob::Kill() {
   if (!transaction_.get())
@@ skipping 565 matching lines @@
       // a response.  When done, we'll record histograms via SDCH_DECODE or
       // SDCH_PASSTHROUGH.  Hence we need to record packet arrival times.
       EnablePacketCounting(kSdchPacketHistogramCount);
     }
   }
 
   URLRequestContext* context = request_->context();
   if (context) {
     // Only add default Accept-Language and Accept-Charset if the request
     // didn't have them specified.
-    if (!request_info_.extra_headers.HasHeader(
-        HttpRequestHeaders::kAcceptLanguage)) {
-      request_info_.extra_headers.SetHeader(
-          HttpRequestHeaders::kAcceptLanguage,
-          context->accept_language());
-    }
-    if (!request_info_.extra_headers.HasHeader(
-        HttpRequestHeaders::kAcceptCharset)) {
-      request_info_.extra_headers.SetHeader(
-          HttpRequestHeaders::kAcceptCharset,
-          context->accept_charset());
-    }
+    request_info_.extra_headers.SetHeaderIfMissing(
+        HttpRequestHeaders::kAcceptLanguage,
+        context->accept_language());
+    request_info_.extra_headers.SetHeaderIfMissing(
+        HttpRequestHeaders::kAcceptCharset,
+        context->accept_charset());
   }
 }
 
 void URLRequestHttpJob::AddCookieHeaderAndStart() {
   // No matter what, we want to report our status as IO pending since we will
   // be notifying our consumer asynchronously via OnStartCompleted.
   SetStatus(URLRequestStatus(URLRequestStatus::IO_PENDING, 0));
 
   AddRef();  // Balanced in OnCanGetCookiesCompleted
 
@@ skipping 155 matching lines @@
                                     include_subdomains,
                                     ctx->transport_security_state());
     if (!prober->ProbeHost(request_info_.url.host(), request()->context(),
                            delegate)) {
       delete delegate;
     }
   }
 }
 
 }  // namespace net