Upload UMA data using protocol buffers.

chrome/common/metrics/proto/chrome_user_metrics_extension.proto

 // 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.
 //
 // Protocol buffer for Chrome UMA (User Metrics Analysis).
 
 syntax = "proto2";
 
 option optimize_for = LITE_RUNTIME;
 
 package metrics;
 
 import "histogram_event.proto";
 import "omnibox_event.proto";
 import "system_profile.proto";
 import "user_action_event.proto";
 
 // Next tag: 7
 message ChromeUserMetricsExtension {
   // The id of the browser installation that generated these events.
   // Technically, this id is unique to a top-level (one level above the
   // "Default" directory) Chrome user data directory [1], and so is shared among
   // all Chrome user profiles contained in this user data directory.
-  // A UserID of 0 is reserved for test data (monitoring and internal testing)
-  // and should normally be ignored in analysis of the data.
+  // An id of 0 is reserved for test data (monitoring and internal testing) and
+  // should normally be ignored in analysis of the data.
   // [1] http://www.chromium.org/user-experience/user-data-directory
-  optional fixed64 user_id = 1;
+  optional fixed64 client_id = 1;
 
   // The session id for this user.
   // Values such as tab ids are only meaningful within a particular session.
   // The client keeps track of the session id and sends it with each event.
   // The session id is simply an integer that is incremented each time the user
   // relaunches Chrome.
   optional int32 session_id = 2;
 
   // Information about the user's browser and system configuration.
   optional SystemProfileProto system_profile = 3;
 
   // This message will log one or more of the following event types:
   repeated UserActionEventProto user_action_event = 4;
   repeated OmniboxEventProto omnibox_event = 5;
   repeated HistogramEventProto histogram_event = 6;
 }