Maybe add CORS headers to data reduction proxy redirect

components/data_reduction_proxy/browser/data_reduction_proxy_protocol.cc

 // Copyright 2014 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 "components/data_reduction_proxy/browser/data_reduction_proxy_protocol.h"
 
 #include "base/memory/ref_counted.h"
 #include "base/time/time.h"
 #include "components/data_reduction_proxy/browser/data_reduction_proxy_params.h"
 #include "components/data_reduction_proxy/browser/data_reduction_proxy_tamper_detection.h"
@@ skipping 164 matching lines @@
 
   request->SetLoadFlags(request->load_flags() |
                         net::LOAD_DISABLE_CACHE |
                         net::LOAD_BYPASS_PROXY);
   *override_response_headers = new net::HttpResponseHeaders(
       original_response_headers->raw_headers());
   (*override_response_headers)->ReplaceStatusLine("HTTP/1.1 302 Found");
   (*override_response_headers)->RemoveHeader("Location");
   (*override_response_headers)->AddHeader("Location: " +
                                           request->url().spec());
+  std::string http_origin;
+  const net::HttpRequestHeaders& request_headers =
+      request->extra_request_headers();
+  if (request_headers.GetHeader("Origin", &http_origin)) {
+    // If this redirect is used in a cross-origin request, add CORS headers to
+    // make sure that the redirect gets through. Note that the destination URL
+    // is still subject to the usual CORS policy, i.e. the resource will only
+    // be available to web pages if the server serves the response with the
+    // required CORS response headers.
+    (*override_response_headers)->AddHeader(
+        "Access-Control-Allow-Origin: " + http_origin);
+    (*override_response_headers)->AddHeader(
+        "Access-Control-Allow-Credentials: true");
+  }
   // TODO(bengr): Should we pop_back the request->url_chain?
 }
 
 void MarkProxiesAsBadUntil(
     net::URLRequest* request,
     base::TimeDelta& bypass_duration,
     bool bypass_all,
     const std::pair<GURL, GURL>& data_reduction_proxies) {
   DCHECK(!data_reduction_proxies.first.is_empty());
   // Synthesize a suitable |ProxyInfo| to add the proxies to the
@@ skipping 17 matching lines @@
   net::ProxyService* proxy_service = request->context()->proxy_service();
   DCHECK(proxy_service);
 
   proxy_service->MarkProxiesAsBadUntil(proxy_info,
                                        bypass_duration,
                                        fallback,
                                        request->net_log());
 }
 
 }  // namespace data_reduction_proxy