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 103269)
+++ 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"
@@ -544,6 +546,14 @@
   if (install_cause() == extension_misc::INSTALL_CAUSE_USER_DOWNLOAD) {
     UserMetrics::RecordAction(
         UserMetricsAction("Extensions.ExtensionInstalled"));
+
+    static bool default_apps_trial_exists =
+        base::FieldTrialList::TrialExists(kDefaultAppsTrial_Name);
+    if (default_apps_trial_exists) {
+      UserMetrics::RecordComputedAction(
+          base::FieldTrial::MakeName("Extensions.ExtensionInstalled",
+                                     kDefaultAppsTrial_Name));

[asargent_no_longer_on_chrome, 2011/09/29 20:46:29]

You might consider adding the following towards the top of the .cc file:

using base::FieldTrial;
using base::FieldTrialList;

Then this code can just be:

if (FieldTrialList::TrialExists(kDefaultAppsTrial_Name)) {
  UserMetrics::RecordComputedAction(
      FieldTrial::MakeName("Extensions.ExtensionInstalled",
                           kDefaultAppsTrial_Name));
}

(If you choose to do it that way here, do the same thing in extension_service.cc
too). 

Your call either way.

[Roger Tawa OOO till Jul 10th, 2011/09/29 22:17:38]

If its my call, then I'll leave it as is.  I don't really like using 'using' :-)
 Independently of this, I would not change the code to be as you described
because I want the return value of TrialExists to be assigned to a local static
bool.  This is the same pattern used in all field trial code.

+    }
   }
 
   if (!BrowserThread::PostTask(