Add UMA for the app list doodle being clicked.

chrome/browser/ui/webui/app_list/start_page_handler.cc

Index: chrome/browser/ui/webui/app_list/start_page_handler.cc
diff --git a/chrome/browser/ui/webui/app_list/start_page_handler.cc b/chrome/browser/ui/webui/app_list/start_page_handler.cc
index 124914b74c91e32453bcfab308d11f3e6977f50f..6baee3959a17d7cff33eb994269fd4c29ecd0248 100644
--- a/chrome/browser/ui/webui/app_list/start_page_handler.cc
+++ b/chrome/browser/ui/webui/app_list/start_page_handler.cc
@@ -8,6 +8,7 @@
 
 #include "base/bind.h"
 #include "base/memory/scoped_ptr.h"
+#include "base/metrics/histogram.h"
 #include "base/values.h"
 #include "base/version.h"
 #include "chrome/browser/profiles/profile.h"
@@ -47,6 +48,9 @@ StartPageHandler::~StartPageHandler() {
 
 void StartPageHandler::RegisterMessages() {
   web_ui()->RegisterMessageCallback(
+      "doodleClicked", base::Bind(&StartPageHandler::HandleDoodleClicked,
+                                  base::Unretained(this)));
+  web_ui()->RegisterMessageCallback(
       "initialize",
       base::Bind(&StartPageHandler::HandleInitialize, base::Unretained(this)));
   web_ui()->RegisterMessageCallback(
@@ -113,6 +117,10 @@ void StartPageHandler::OnHotwordEnabledChanged() {
 }
 #endif
 
+void StartPageHandler::HandleDoodleClicked(const base::ListValue* args) {
+  UMA_HISTOGRAM_ENUMERATION("Apps.AppListDoodleClicked", 1, 2);

[Alexei Svitkine (slow), 2015/02/19 14:56:23]

Please use UMA_HISTOGRAM_BOOLEAN(), which produces the same result.

+}
+
 void StartPageHandler::HandleInitialize(const base::ListValue* args) {
   Profile* profile = Profile::FromWebUI(web_ui());
   StartPageService* service = StartPageService::Get(profile);