Add metrics to help measure effects of installing default apps in a profile.

chrome/browser/extensions/crx_installer.cc

Index: chrome/browser/extensions/crx_installer.cc
===================================================================
--- chrome/browser/extensions/crx_installer.cc	(revision 105209)
+++ chrome/browser/extensions/crx_installer.cc	(working copy)
@@ -9,6 +9,7 @@
 
 #include "base/file_util.h"
 #include "base/lazy_instance.h"
+#include "base/metrics/field_trial.h"
 #include "base/metrics/histogram.h"
 #include "base/path_service.h"
 #include "base/scoped_temp_dir.h"
@@ -22,6 +23,7 @@
 #include "chrome/browser/browser_process.h"
 #include "chrome/browser/extensions/convert_user_script.h"
 #include "chrome/browser/extensions/convert_web_app.h"
+#include "chrome/browser/extensions/default_apps_trial.h"
 #include "chrome/browser/extensions/extension_error_reporter.h"
 #include "chrome/browser/extensions/extension_service.h"
 #include "chrome/browser/shell_integration.h"
@@ -542,8 +544,16 @@
 
   // Tracking number of extensions installed by users
   if (install_cause() == extension_misc::INSTALL_CAUSE_USER_DOWNLOAD) {
-    UserMetrics::RecordAction(
-        UserMetricsAction("Extensions.ExtensionInstalled"));
+    UMA_HISTOGRAM_ENUMERATION("Extensions.ExtensionInstalled", 1, 2);
+
+    static bool default_apps_trial_exists =
+        base::FieldTrialList::TrialExists(kDefaultAppsTrial_Name);
+    if (default_apps_trial_exists) {
+      UMA_HISTOGRAM_ENUMERATION(
+          base::FieldTrial::MakeName("Extensions.ExtensionInstalled",
+                                     kDefaultAppsTrial_Name),
+          1, 2);
+    }
   }
 
   if (!BrowserThread::PostTask(