Fix UpdateClient XML serialization when <disabled> reasons are present.

The buggy code serializes the <disabled> tag before closing the
<app> tag, like this:

<app appid=...version="0.9" brand="TEST" enabled="0"<disabled reason="0"/>

Bug: 901497
Change-Id: I2106ee35e99dd9c7fa66baab0c0efdc4942cab05
Reviewed-on: https://chromium-review.googlesource.com/c/1316441Reviewed-by: Minh Nguyen <mxnguyen@chromium.org>
Commit-Queue: Sorin Jianu <sorin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#605113}

components/update_client/protocol_serializer_xml.cc

@@ -96,6 +96,7 @@ std::string ProtocolSerializerXml::Serialize(
 #endif
 
   for (const auto& app : request.apps) {
+    // Begin <app> attributes.
     base::StringAppendF(&msg, "<app appid=\"%s\"", app.app_id.c_str());
     base::StringAppendF(&msg, " version=\"%s\"", app.version.c_str());
     if (!app.brand_code.empty())
@@ -118,16 +119,16 @@ std::string ProtocolSerializerXml::Serialize(
       base::StringAppendF(&msg, " cohortname=\"%s\"", app.cohort_name.c_str());
     if (!app.cohort_hint.empty())
       base::StringAppendF(&msg, " cohorthint=\"%s\"", app.cohort_hint.c_str());
-
     if (app.enabled)
       base::StringAppendF(&msg, " enabled=\"%d\"", *app.enabled ? 1 : 0);
+    base::StringAppendF(&msg, ">");
+    // End <app> attributes.
+
     if (app.disabled_reasons) {
       for (const int disabled_reason : *app.disabled_reasons)
         base::StringAppendF(&msg, "<disabled reason=\"%d\"/>", disabled_reason);
     }
 
-    base::StringAppendF(&msg, ">");
-
     if (app.update_check) {
       base::StringAppendF(&msg, "<updatecheck");
       if (app.update_check->is_update_disabled)
@@ -186,6 +187,7 @@ std::string ProtocolSerializerXml::Serialize(
         base::StringAppendF(&msg, "/>");
       }
     }
+
     base::StringAppendF(&msg, "</app>");
   }