Fix the broken XML parser due to version mismatch.

components/update_client/utils.cc

Index: components/update_client/utils.cc
diff --git a/components/update_client/utils.cc b/components/update_client/utils.cc
index 93d7ac097e7cbbcc7ce5d8e876635527076533a1..96e15a97c98a888990bd3c94f8ea93db468e8829 100644
--- a/components/update_client/utils.cc
+++ b/components/update_client/utils.cc
@@ -32,6 +32,7 @@
 #include "components/update_client/update_client.h"
 #include "components/update_client/update_client_errors.h"
 #include "components/update_client/update_query_params.h"
+#include "components/update_client/update_response.h"
 #include "components/update_client/updater_state.h"
 #include "crypto/secure_hash.h"
 #include "crypto/sha2.h"
@@ -95,9 +96,7 @@ std::string GetServicePack() {
 
 }  // namespace
 
-// Builds a protocol message. The protocol versions so far are:
-// * Version 3.1: it changes how the run actions are serialized.
-// * Version 3.0: it is the version implemented by the desktop updaters.
+// Builds a protocol message.
 std::string BuildProtocolRequest(
     const std::string& prod_id,
     const std::string& browser_version,
@@ -108,9 +107,10 @@ std::string BuildProtocolRequest(
     const std::string& request_body,
     const std::string& additional_attributes,
     const std::unique_ptr<UpdaterState::Attributes>& updater_state_attributes) {
-  std::string request(
+  std::string request = base::StringPrintf(
       "<?xml version=\"1.0\" encoding=\"UTF-8\"?>"
-      "<request protocol=\"3.1\" ");
+      "<request protocol=\"%s\" ",
+      kProtocolVersion);
 
   if (!additional_attributes.empty())
     base::StringAppendF(&request, "%s ", additional_attributes.c_str());