Add UMA histograms for WebUSB.

chrome/browser/chrome_webusb_browser_client.cc

Index: chrome/browser/chrome_webusb_browser_client.cc
diff --git a/chrome/browser/chrome_webusb_browser_client.cc b/chrome/browser/chrome_webusb_browser_client.cc
index 24a63f29f81320b87f1cac3260878c09647449f0..29428149f1eb0c6898b9aefc55eb4db594bfcd3c 100644
--- a/chrome/browser/chrome_webusb_browser_client.cc
+++ b/chrome/browser/chrome_webusb_browser_client.cc
@@ -7,6 +7,7 @@
 #include <utility>
 
 #include "base/macros.h"
+#include "base/metrics/histogram_macros.h"
 #include "base/strings/utf_string_conversions.h"
 #include "chrome/browser/net/referrer.h"
 #include "chrome/browser/profiles/profile_manager.h"
@@ -30,6 +31,23 @@ namespace {
 
 const char kWebUsbDetectorNotificationID[] = "webusb.detector";
 
+enum WebUsbNotificationClosed {

[asargent_no_longer_on_chrome, 2016/01/21 18:54:15]

nit: We typically include a comment above enums used in histograms warning
people not to remove/reorder/renumber items in them; it would be good to do so
here. (You can search around the extensions system for similar comments and crib
their form or whatever)

(same comment applies to new enums in other files in the CL)

+  // The notification was dismissed but not by the user (either automatically
+  // or because the device was unplugged).
+  WEBUSB_NOTIFICATION_CLOSED,
+  // The user closed the notification.
+  WEBUSB_NOTIFICATION_CLOSED_BY_USER,
+  // The user clicked on the notification.
+  WEBUSB_NOTIFICATION_CLOSED_CLICKED,
+  // Maximum value for the enum.
+  WEBUSB_NOTIFICATION_CLOSED_MAX
+};
+
+void RecordNotificationClosure(WebUsbNotificationClosed disposition) {
+  UMA_HISTOGRAM_ENUMERATION("WebUsb.NotificationClosed", disposition,
+                            WEBUSB_NOTIFICATION_CLOSED_MAX);
+}
+
 Browser* GetBrowser() {
   chrome::ScopedTabbedBrowserDisplayer browser_displayer(
       ProfileManager::GetActiveUserProfile(), chrome::GetActiveDesktop());
@@ -51,16 +69,27 @@ class WebUsbNotificationDelegate : public message_center::NotificationDelegate {
       : landing_page_(landing_page), notification_id_(notification_id) {}
 
   void Click() override {
+    clicked_ = true;
     OpenURL(landing_page_);
     message_center::MessageCenter::Get()->RemoveNotification(
         notification_id_, false /* by_user */);
   }
 
+  void Close(bool by_user) override {
+    if (clicked_)
+      RecordNotificationClosure(WEBUSB_NOTIFICATION_CLOSED_CLICKED);
+    else if (by_user)
+      RecordNotificationClosure(WEBUSB_NOTIFICATION_CLOSED_BY_USER);
+    else
+      RecordNotificationClosure(WEBUSB_NOTIFICATION_CLOSED);
+  }
+
  private:
   ~WebUsbNotificationDelegate() override = default;
 
   GURL landing_page_;
   std::string notification_id_;
+  bool clicked_ = false;
 
   DISALLOW_COPY_AND_ASSIGN(WebUsbNotificationDelegate);
 };