GCAPI should append to the existing experiment_labels instead of clobbering them.

chrome/installer/gcapi/gcapi_test.cc

Index: chrome/installer/gcapi/gcapi_test.cc
diff --git a/chrome/installer/gcapi/gcapi_test.cc b/chrome/installer/gcapi/gcapi_test.cc
index 68633e0a93a6d6434dae1412154e3a9bfd793a75..477b15a98ea7bac58eef52cbb6ba2d99ed47dbe0 100644
--- a/chrome/installer/gcapi/gcapi_test.cc
+++ b/chrome/installer/gcapi/gcapi_test.cc
@@ -4,6 +4,7 @@
 
 #include <stdio.h>
 
+#include "base/at_exit.h"
 #include "base/command_line.h"
 #include "chrome/installer/gcapi/gcapi.h"
 #include "testing/gtest/include/gtest/gtest.h"
@@ -60,6 +61,7 @@ void call_dynamically() {
 const char kManualLaunchTests[] = "launch-chrome";
 
 int main(int argc, char* argv[]) {
+  base::AtExitManager exit_manager;
   CommandLine::Init(argc, argv);
 
   testing::InitGoogleTest(&argc, argv);