Add metrics for interactions with the Apps Launcher promo dialog.

chrome/browser/ui/webui/ntp/app_launcher_handler.cc

Index: chrome/browser/ui/webui/ntp/app_launcher_handler.cc
diff --git a/chrome/browser/ui/webui/ntp/app_launcher_handler.cc b/chrome/browser/ui/webui/ntp/app_launcher_handler.cc
index 88bff10639a3216ebdf90b828ba72f740a440b0c..e3c4e42472b2de8d799751fc395f7944379d66bf 100644
--- a/chrome/browser/ui/webui/ntp/app_launcher_handler.cc
+++ b/chrome/browser/ui/webui/ntp/app_launcher_handler.cc
@@ -6,6 +6,7 @@
 
 #include <vector>
 
+#include "apps/metrics_names.h"
 #include "apps/pref_names.h"
 #include "base/auto_reset.h"
 #include "base/bind.h"
@@ -212,6 +213,9 @@ void AppLauncherHandler::RegisterMessages() {
   web_ui()->RegisterMessageCallback("stopShowingAppLauncherPromo",
       base::Bind(&AppLauncherHandler::StopShowingAppLauncherPromo,
                  base::Unretained(this)));
+  web_ui()->RegisterMessageCallback("onLearnMore",
+      base::Bind(&AppLauncherHandler::OnLearnMore,
+                 base::Unretained(this)));
 }
 
 void AppLauncherHandler::Observe(int type,
@@ -694,6 +698,18 @@ void AppLauncherHandler::StopShowingAppLauncherPromo(
     const base::ListValue* args) {
   g_browser_process->local_state()->SetBoolean(
       apps::prefs::kShowAppLauncherPromo, false);
+  UMA_HISTOGRAM_ENUMERATION(apps::kAppLauncherPromoHistogram,
+                            apps::APP_LAUNCHER_PROMO_DISMISSED,
+                            apps::APP_LAUNCHER_PROMO_MAX);

[Ilya Sherman, 2013/06/25 21:35:15]

I'd strongly recommend creating a method like
apps::LogAppLauncherPromoHistogram(), and just passing in
apps::APP_LAUNCHER_PROMO_DISMISSED from here.  That both reduces the total
number of lines of code, and makes it harder for a single callsite to have a
typo or other easy-to-miss error.

[MAD, 2013/06/26 03:33:40]

Done.

+
+}
+
+void AppLauncherHandler::OnLearnMore(
+    const base::ListValue* args) {
+  UMA_HISTOGRAM_ENUMERATION(apps::kAppLauncherPromoHistogram,
+                            apps::APP_LAUNCHER_PROMO_LEARN_MORE,
+                            apps::APP_LAUNCHER_PROMO_MAX);
+
 }
 
 void AppLauncherHandler::OnFaviconForApp(