Announce to Omaha that Chrome accepts CRX₂ and CRX₃ files.

components/update_client/protocol_builder.cc

 // Copyright 2017 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/update_client/protocol_builder.h"
 
 #include <stdint.h>
 
 #include "base/guid.h"
 #include "base/logging.h"
@@ skipping 164 matching lines @@
     const std::string& additional_attributes,
     const std::unique_ptr<UpdaterState::Attributes>& updater_state_attributes) {
   std::string request = base::StringPrintf(
       "<?xml version=\"1.0\" encoding=\"UTF-8\"?>"
       "<request protocol=\"%s\" ",
       kProtocolVersion);
 
   if (!additional_attributes.empty())
     base::StringAppendF(&request, "%s ", additional_attributes.c_str());
 
+  // Constant information for this updater.
+  base::StringAppendF(&request, "dedup=\"cr\" acceptformat=\"crx2,crx3\" ");
+
   // Chrome version and platform information.
   base::StringAppendF(
       &request,
       "version=\"%s-%s\" prodversion=\"%s\" "
       "requestid=\"{%s}\" lang=\"%s\" updaterchannel=\"%s\" prodchannel=\"%s\" "
       "os=\"%s\" arch=\"%s\" nacl_arch=\"%s\"",
       prod_id.c_str(),  // "version" is prefixed by prod_id.
       browser_version.c_str(),
       browser_version.c_str(),            // "prodversion"
       base::GenerateGUID().c_str(),       // "requestid"
@@ skipping 149 matching lines @@
       base::JoinString(component.events(), "").c_str()));  // events
 
   // The ping request does not include any updater state.
   return BuildProtocolRequest(
       config.GetProdId(), config.GetBrowserVersion().GetString(),
       config.GetChannel(), config.GetLang(), config.GetOSLongName(),
       config.GetDownloadPreference(), app_element, "", nullptr);
 }
 
 }  // namespace update_client