Fix a crashing call to GURL::spec() in downloads_api.cc:DownloadItemToJSON()

chrome/browser/safe_browsing/download_protection_service.cc

 // Copyright (c) 2012 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 "chrome/browser/safe_browsing/download_protection_service.h"
 
 #include "base/bind.h"
 #include "base/compiler_specific.h"
 #include "base/format_macros.h"
 #include "base/memory/scoped_ptr.h"
@@ skipping 176 matching lines @@
   }
 
   void ReportMalware(SBThreatType threat_type) {
     std::string post_data;
     if (!sha256_hash_.empty())
       post_data += base::HexEncode(sha256_hash_.data(),
                                    sha256_hash_.size()) + "\n";
     for (size_t i = 0; i < url_chain_.size(); ++i) {
       post_data += url_chain_[i].spec() + "\n";
     }
+    // Be careful about taking the front()/back() of possibly-empty vectors!
+    // http://crbug.com/190096
+    const GURL& malicious_url = url_chain_.empty() ? GURL::EmptyGURL()
+                                                   : url_chain_.back();
+    const GURL& page_url = url_chain_.empty() ? GURL::EmptyGURL()
+                                              : url_chain_.front();
     ui_manager_->ReportSafeBrowsingHit(
-        url_chain_.back(),  // malicious_url
-        url_chain_.front(), // page_url
+        malicious_url,
+        page_url,
         referrer_url_,
         true,  // is_subresource
         threat_type,
         post_data);
   }
 
   void UpdateDownloadCheckStats(SBStatsType stat_type) {
     UMA_HISTOGRAM_ENUMERATION("SB2.DownloadChecks",
                               stat_type,
                               DOWNLOAD_CHECKS_MAX);
@@ skipping 734 matching lines @@
   std::string url = kDownloadRequestUrl;
   std::string api_key = google_apis::GetAPIKey();
   if (!api_key.empty()) {
     base::StringAppendF(&url, "?key=%s",
                         net::EscapeQueryParamValue(api_key, true).c_str());
   }
   return url;
 }
 
 }  // namespace safe_browsing