Add UMA histograms for WebUSB.

chrome/browser/usb/usb_chooser_context.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/usb/usb_chooser_context.h"
 
 #include <utility>
 #include <vector>
 
+#include "base/metrics/histogram_macros.h"
 #include "base/stl_util.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/values.h"
 #include "chrome/browser/profiles/profile.h"
 #include "device/core/device_client.h"
 #include "device/usb/usb_device.h"
 
 using device::UsbDevice;
 
 namespace {
 
 const char kDeviceNameKey[] = "name";
 const char kGuidKey[] = "ephemeral-guid";
 const char kProductIdKey[] = "product-id";
 const char kSerialNumberKey[] = "serial-number";
 const char kVendorIdKey[] = "vendor-id";
 
+// Reasons a permission may be closed. These are used in histograms so do not
+// remove/reorder entries. Only add at the end just before
+// WEBUSB_PERMISSION_REVOKED_MAX. Also remember to update the enum listing in
+// tools/metrics/histograms/histograms.xml.
+enum WebUsbPermissionRevoked {
+  // Permission to access a USB device was revoked by the user.
+  WEBUSB_PERMISSION_REVOKED = 0,
+  // Permission to access an ephemeral USB device was revoked by the user.
+  WEBUSB_PERMISSION_REVOKED_EPHEMERAL,
+  // Maximum value for the enum.
+  WEBUSB_PERMISSION_REVOKED_MAX
+};
+
+void RecordPermissionRevocation(WebUsbPermissionRevoked kind) {
+  UMA_HISTOGRAM_ENUMERATION("WebUsb.PermissionRevoked", kind,
+                            WEBUSB_PERMISSION_REVOKED_MAX);
+}
+
 bool CanStorePersistentEntry(const scoped_refptr<const UsbDevice>& device) {
   return !device->serial_number().empty();
 }
 
 const base::DictionaryValue* FindForDevice(
     const std::vector<scoped_ptr<base::DictionaryValue>>& device_list,
     const scoped_refptr<const UsbDevice>& device) {
   const std::string utf8_serial_number =
       base::UTF16ToUTF8(device->serial_number());
 
@@ skipping 72 matching lines @@
   return objects;
 }
 
 void UsbChooserContext::RevokeObjectPermission(
     const GURL& requesting_origin,
     const GURL& embedding_origin,
     const base::DictionaryValue& object) {
   std::string guid;
   if (object.GetString(kGuidKey, &guid)) {
     RevokeDevicePermission(requesting_origin, embedding_origin, guid);
+    RecordPermissionRevocation(WEBUSB_PERMISSION_REVOKED_EPHEMERAL);
   } else {
     ChooserContextBase::RevokeObjectPermission(requesting_origin,
                                                embedding_origin, object);
+    RecordPermissionRevocation(WEBUSB_PERMISSION_REVOKED);
   }
 }
 
 void UsbChooserContext::GrantDevicePermission(const GURL& requesting_origin,
                                               const GURL& embedding_origin,
                                               const std::string& guid) {
   scoped_refptr<UsbDevice> device = usb_service_->GetDevice(guid);
   if (!device)
     return;
 
@@ skipping 53 matching lines @@
 bool UsbChooserContext::IsValidObject(const base::DictionaryValue& object) {
   return object.size() == 4 && object.HasKey(kDeviceNameKey) &&
          object.HasKey(kVendorIdKey) && object.HasKey(kProductIdKey) &&
          object.HasKey(kSerialNumberKey);
 }
 
 void UsbChooserContext::OnDeviceRemoved(scoped_refptr<UsbDevice> device) {
   for (auto& map_entry : ephemeral_devices_)
     map_entry.second.erase(device->guid());
 }