Set up the infrastructure for Extension event metrics.

extensions/browser/extension_event_histogram_value.h

Index: extensions/browser/extension_event_histogram_value.h
diff --git a/extensions/browser/extension_event_histogram_value.h b/extensions/browser/extension_event_histogram_value.h
new file mode 100644
index 0000000000000000000000000000000000000000..7f18b92965c67f7c2396d48cf0e2756721892585
--- /dev/null
+++ b/extensions/browser/extension_event_histogram_value.h
@@ -0,0 +1,353 @@
+// 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.
+
+#ifndef EXTENSIONS_BROWSER_EXTENSION_EVENT_HISTOGRAM_VALUE_H_
+#define EXTENSIONS_BROWSER_EXTENSION_EVENT_HISTOGRAM_VALUE_H_
+
+namespace extensions {
+namespace events {
+
+// TODO(kalman): I am still in the process of migrating Event construction away
+// from using "UNKNOWN" to their real histogram values. See crbug.com/503402.
+//
+// Short version:
+//  *Never* reorder or delete entries in the |HistogramValue| enumeration.
+//  When creating a new extension event, add a new entry at the end of the
+//  enum, just prior to ENUM_BOUNDARY.
+//
+// Long version: See extension_function_histogram_value.h
+enum HistogramValue {
+  UNKNOWN = 0,
+  ACCESSIBILITY_PRIVATE_ON_INTRODUCE_CHROME_VOX,
+  ACTIVITY_LOG_PRIVATE_ON_EXTENSION_ACTIVITY,
+  ALARMS_ON_ALARM,
+  APP_CURRENT_WINDOW_INTERNAL_ON_ALPHA_ENABLED_CHANGED,
+  APP_CURRENT_WINDOW_INTERNAL_ON_BOUNDS_CHANGED,
+  APP_CURRENT_WINDOW_INTERNAL_ON_CLOSED,
+  APP_CURRENT_WINDOW_INTERNAL_ON_FULLSCREENED,
+  APP_CURRENT_WINDOW_INTERNAL_ON_MAXIMIZED,
+  APP_CURRENT_WINDOW_INTERNAL_ON_MINIMIZED,
+  APP_CURRENT_WINDOW_INTERNAL_ON_RESTORED,
+  APP_CURRENT_WINDOW_INTERNAL_ON_WINDOW_SHOWN_FOR_TESTS,
+  APP_RUNTIME_ON_EMBED_REQUESTED,
+  APP_RUNTIME_ON_LAUNCHED,
+  APP_RUNTIME_ON_RESTARTED,
+  APP_WINDOW_ON_BOUNDS_CHANGED,
+  APP_WINDOW_ON_CLOSED,
+  APP_WINDOW_ON_FULLSCREENED,
+  APP_WINDOW_ON_MAXIMIZED,
+  APP_WINDOW_ON_MINIMIZED,
+  APP_WINDOW_ON_RESTORED,
+  AUDIO_MODEM_ON_RECEIVED,
+  AUDIO_MODEM_ON_TRANSMIT_FAIL,
+  AUDIO_ON_DEVICE_CHANGED,
+  AUDIO_ON_DEVICES_CHANGED,
+  AUDIO_ON_LEVEL_CHANGED,
+  AUDIO_ON_MUTE_CHANGED,
+  AUTOFILL_PRIVATE_ON_ADDRESS_LIST_CHANGED,
+  AUTOFILL_PRIVATE_ON_CREDIT_CARD_LIST_CHANGED,
+  AUTOMATION_INTERNAL_ON_ACCESSIBILITY_EVENT,
+  AUTOMATION_INTERNAL_ON_ACCESSIBILITY_TREE_DESTROYED,
+  BLUETOOTH_LOW_ENERGY_ON_CHARACTERISTIC_VALUE_CHANGED,
+  BLUETOOTH_LOW_ENERGY_ON_DESCRIPTOR_VALUE_CHANGED,
+  BLUETOOTH_LOW_ENERGY_ON_SERVICE_ADDED,
+  BLUETOOTH_LOW_ENERGY_ON_SERVICE_CHANGED,
+  BLUETOOTH_LOW_ENERGY_ON_SERVICE_REMOVED,
+  BLUETOOTH_ON_ADAPTER_STATE_CHANGED,
+  BLUETOOTH_ON_DEVICE_ADDED,
+  BLUETOOTH_ON_DEVICE_CHANGED,
+  BLUETOOTH_ON_DEVICE_REMOVED,
+  BLUETOOTH_PRIVATE_ON_PAIRING,
+  BLUETOOTH_SOCKET_ON_ACCEPT,
+  BLUETOOTH_SOCKET_ON_ACCEPT_ERROR,
+  BLUETOOTH_SOCKET_ON_RECEIVE,
+  BLUETOOTH_SOCKET_ON_RECEIVE_ERROR,
+  BOOKMARK_MANAGER_PRIVATE_ON_DRAG_ENTER,
+  BOOKMARK_MANAGER_PRIVATE_ON_DRAG_LEAVE,
+  BOOKMARK_MANAGER_PRIVATE_ON_DROP,
+  BOOKMARK_MANAGER_PRIVATE_ON_META_INFO_CHANGED,
+  BOOKMARKS_ON_CHANGED,
+  BOOKMARKS_ON_CHILDREN_REORDERED,
+  BOOKMARKS_ON_CREATED,
+  BOOKMARKS_ON_IMPORT_BEGAN,
+  BOOKMARKS_ON_IMPORT_ENDED,
+  BOOKMARKS_ON_MOVED,
+  BOOKMARKS_ON_REMOVED,
+  BRAILLE_DISPLAY_PRIVATE_ON_DISPLAY_STATE_CHANGED,
+  BRAILLE_DISPLAY_PRIVATE_ON_KEY_EVENT,
+  BROWSER_ACTION_ON_CLICKED,
+  CAST_STREAMING_RTP_STREAM_ON_ERROR,
+  CAST_STREAMING_RTP_STREAM_ON_STARTED,
+  CAST_STREAMING_RTP_STREAM_ON_STOPPED,
+  COMMANDS_ON_COMMAND,
+  CONTEXT_MENUS_INTERNAL_ON_CLICKED,
+  CONTEXT_MENUS_ON_CLICKED,
+  COOKIES_ON_CHANGED,
+  COPRESENCE_ON_MESSAGES_RECEIVED,
+  COPRESENCE_ON_STATUS_UPDATED,
+  COPRESENCE_PRIVATE_ON_CONFIG_AUDIO,
+  COPRESENCE_PRIVATE_ON_DECODE_SAMPLES_REQUEST,
+  COPRESENCE_PRIVATE_ON_ENCODE_TOKEN_REQUEST,
+  DEBUGGER_ON_DETACH,
+  DEBUGGER_ON_EVENT,
+  DECLARATIVE_CONTENT_ON_PAGE_CHANGED,
+  DECLARATIVE_WEB_REQUEST_ON_MESSAGE,
+  DECLARATIVE_WEB_REQUEST_ON_REQUEST,
+  DEVELOPER_PRIVATE_ON_ITEM_STATE_CHANGED,
+  DEVELOPER_PRIVATE_ON_PROFILE_STATE_CHANGED,
+  DEVTOOLS_INSPECTED_WINDOW_ON_RESOURCE_ADDED,
+  DEVTOOLS_INSPECTED_WINDOW_ON_RESOURCE_CONTENT_COMMITTED,
+  DEVTOOLS_NETWORK_ON_NAVIGATED,
+  DEVTOOLS_NETWORK_ON_REQUEST_FINISHED,
+  DOWNLOADS_ON_CHANGED,
+  DOWNLOADS_ON_CREATED,
+  DOWNLOADS_ON_DETERMINING_FILENAME,
+  DOWNLOADS_ON_ERASED,
+  EASY_UNLOCK_PRIVATE_ON_START_AUTO_PAIRING,
+  EASY_UNLOCK_PRIVATE_ON_USER_INFO_UPDATED,
+  EXPERIENCE_SAMPLING_PRIVATE_ON_DECISION,
+  EXPERIENCE_SAMPLING_PRIVATE_ON_DISPLAYED,
+  EXPERIMENTAL_DEVTOOLS_CONSOLE_ON_MESSAGE_ADDED,
+  EXTENSION_ON_REQUEST,
+  EXTENSION_ON_REQUEST_EXTERNAL,
+  EXTENSION_OPTIONS_INTERNAL_ON_CLOSE,
+  EXTENSION_OPTIONS_INTERNAL_ON_LOAD,
+  EXTENSION_OPTIONS_INTERNAL_ON_PREFERRED_SIZE_CHANGED,
+  FEEDBACK_PRIVATE_ON_FEEDBACK_REQUESTED,
+  FILE_BROWSER_HANDLER_ON_EXECUTE,
+  FILE_MANAGER_PRIVATE_ON_COPY_PROGRESS,
+  FILE_MANAGER_PRIVATE_ON_DEVICE_CHANGED,
+  FILE_MANAGER_PRIVATE_ON_DIRECTORY_CHANGED,
+  FILE_MANAGER_PRIVATE_ON_DRIVE_CONNECTION_STATUS_CHANGED,
+  FILE_MANAGER_PRIVATE_ON_DRIVE_SYNC_ERROR,
+  FILE_MANAGER_PRIVATE_ON_FILE_TRANSFERS_UPDATED,
+  FILE_MANAGER_PRIVATE_ON_MOUNT_COMPLETED,
+  FILE_MANAGER_PRIVATE_ON_PREFERENCES_CHANGED,
+  FILE_SYSTEM_ON_VOLUME_LIST_CHANGED,
+  FILE_SYSTEM_PROVIDER_ON_ABORT_REQUESTED,
+  FILE_SYSTEM_PROVIDER_ON_ADD_WATCHER_REQUESTED,
+  FILE_SYSTEM_PROVIDER_ON_CLOSE_FILE_REQUESTED,
+  FILE_SYSTEM_PROVIDER_ON_CONFIGURE_REQUESTED,
+  FILE_SYSTEM_PROVIDER_ON_COPY_ENTRY_REQUESTED,
+  FILE_SYSTEM_PROVIDER_ON_CREATE_DIRECTORY_REQUESTED,
+  FILE_SYSTEM_PROVIDER_ON_CREATE_FILE_REQUESTED,
+  FILE_SYSTEM_PROVIDER_ON_DELETE_ENTRY_REQUESTED,
+  FILE_SYSTEM_PROVIDER_ON_GET_METADATA_REQUESTED,
+  FILE_SYSTEM_PROVIDER_ON_MOUNT_REQUESTED,
+  FILE_SYSTEM_PROVIDER_ON_MOVE_ENTRY_REQUESTED,
+  FILE_SYSTEM_PROVIDER_ON_OPEN_FILE_REQUESTED,
+  FILE_SYSTEM_PROVIDER_ON_READ_DIRECTORY_REQUESTED,
+  FILE_SYSTEM_PROVIDER_ON_READ_FILE_REQUESTED,
+  FILE_SYSTEM_PROVIDER_ON_REMOVE_WATCHER_REQUESTED,
+  FILE_SYSTEM_PROVIDER_ON_TRUNCATE_REQUESTED,
+  FILE_SYSTEM_PROVIDER_ON_UNMOUNT_REQUESTED,
+  FILE_SYSTEM_PROVIDER_ON_WRITE_FILE_REQUESTED,
+  FONT_SETTINGS_ON_DEFAULT_FIXED_FONT_SIZE_CHANGED,
+  FONT_SETTINGS_ON_DEFAULT_FONT_SIZE_CHANGED,
+  FONT_SETTINGS_ON_FONT_CHANGED,
+  FONT_SETTINGS_ON_MINIMUM_FONT_SIZE_CHANGED,
+  GCD_PRIVATE_ON_DEVICE_REMOVED,
+  GCD_PRIVATE_ON_DEVICE_STATE_CHANGED,
+  GCM_ON_MESSAGE,
+  GCM_ON_MESSAGES_DELETED,
+  GCM_ON_SEND_ERROR,
+  HANGOUTS_PRIVATE_ON_HANGOUT_REQUESTED,
+  HID_ON_DEVICE_ADDED,
+  HID_ON_DEVICE_REMOVED,
+  HISTORY_ON_VISITED,
+  HISTORY_ON_VISIT_REMOVED,
+  HOTWORD_PRIVATE_ON_DELETE_SPEAKER_MODEL,
+  HOTWORD_PRIVATE_ON_ENABLED_CHANGED,
+  HOTWORD_PRIVATE_ON_FINALIZE_SPEAKER_MODEL,
+  HOTWORD_PRIVATE_ON_HOTWORD_SESSION_REQUESTED,
+  HOTWORD_PRIVATE_ON_HOTWORD_SESSION_STOPPED,
+  HOTWORD_PRIVATE_ON_HOTWORD_TRIGGERED,
+  HOTWORD_PRIVATE_ON_MICROPHONE_STATE_CHANGED,
+  HOTWORD_PRIVATE_ON_SPEAKER_MODEL_EXISTS,
+  HOTWORD_PRIVATE_ON_SPEAKER_MODEL_SAVED,
+  IDENTITY_ON_SIGN_IN_CHANGED,
+  IDENTITY_PRIVATE_ON_WEB_FLOW_REQUEST,
+  IDLE_ON_STATE_CHANGED,
+  IMAGE_WRITER_PRIVATE_ON_DEVICE_INSERTED,
+  IMAGE_WRITER_PRIVATE_ON_DEVICE_REMOVED,
+  IMAGE_WRITER_PRIVATE_ON_WRITE_COMPLETE,
+  IMAGE_WRITER_PRIVATE_ON_WRITE_ERROR,
+  IMAGE_WRITER_PRIVATE_ON_WRITE_PROGRESS,
+  INPUT_IME_ON_ACTIVATE,
+  INPUT_IME_ON_BLUR,
+  INPUT_IME_ON_CANDIDATE_CLICKED,
+  INPUT_IME_ON_DEACTIVATED,
+  INPUT_IME_ON_FOCUS,
+  INPUT_IME_ON_INPUT_CONTEXT_UPDATE,
+  INPUT_IME_ON_KEY_EVENT,
+  INPUT_IME_ON_MENU_ITEM_ACTIVATED,
+  INPUT_IME_ON_RESET,
+  INPUT_IME_ON_SURROUNDING_TEXT_CHANGED,
+  INPUT_METHOD_PRIVATE_ON_CHANGED,
+  INPUT_METHOD_PRIVATE_ON_COMPOSITION_BOUNDS_CHANGED,
+  INPUT_METHOD_PRIVATE_ON_DICTIONARY_CHANGED,
+  INPUT_METHOD_PRIVATE_ON_DICTIONARY_LOADED,
+  INSTANCE_ID_ON_TOKEN_REFRESH,
+  LOCATION_ON_LOCATION_ERROR,
+  LOCATION_ON_LOCATION_UPDATE,
+  LOG_PRIVATE_ON_CAPTURED_EVENTS,
+  MANAGEMENT_ON_DISABLED,
+  MANAGEMENT_ON_ENABLED,
+  MANAGEMENT_ON_INSTALLED,
+  MANAGEMENT_ON_UNINSTALLED,
+  MDNS_ON_SERVICE_LIST,
+  MEDIA_GALLERIES_ON_GALLERY_CHANGED,
+  MEDIA_GALLERIES_ON_SCAN_PROGRESS,
+  MEDIA_PLAYER_PRIVATE_ON_NEXT_TRACK,
+  MEDIA_PLAYER_PRIVATE_ON_PREV_TRACK,
+  MEDIA_PLAYER_PRIVATE_ON_TOGGLE_PLAY_STATE,
+  NETWORKING_CONFIG_ON_CAPTIVE_PORTAL_DETECTED,
+  NETWORKING_PRIVATE_ON_DEVICE_STATE_LIST_CHANGED,
+  NETWORKING_PRIVATE_ON_NETWORK_LIST_CHANGED,
+  NETWORKING_PRIVATE_ON_NETWORKS_CHANGED,
+  NETWORKING_PRIVATE_ON_PORTAL_DETECTION_COMPLETED,
+  NOTIFICATION_PROVIDER_ON_CLEARED,
+  NOTIFICATION_PROVIDER_ON_CREATED,
+  NOTIFICATION_PROVIDER_ON_UPDATED,
+  NOTIFICATIONS_ON_BUTTON_CLICKED,
+  NOTIFICATIONS_ON_CLICKED,
+  NOTIFICATIONS_ON_CLOSED,
+  NOTIFICATIONS_ON_PERMISSION_LEVEL_CHANGED,
+  NOTIFICATIONS_ON_SHOW_SETTINGS,
+  OMNIBOX_ON_INPUT_CANCELLED,
+  OMNIBOX_ON_INPUT_CHANGED,
+  OMNIBOX_ON_INPUT_ENTERED,
+  OMNIBOX_ON_INPUT_STARTED,
+  PAGE_ACTION_ON_CLICKED,
+  PASSWORDS_PRIVATE_ON_PASSWORD_EXCEPTIONS_LIST_CHANGED,
+  PASSWORDS_PRIVATE_ON_PLAINTEXT_PASSWORD_RETRIEVED,
+  PASSWORDS_PRIVATE_ON_SAVED_PASSWORDS_LIST_CHANGED,
+  PERMISSIONS_ON_ADDED,
+  PERMISSIONS_ON_REMOVED,
+  PRINTER_PROVIDER_ON_GET_CAPABILITY_REQUESTED,
+  PRINTER_PROVIDER_ON_GET_PRINTERS_REQUESTED,
+  PRINTER_PROVIDER_ON_GET_USB_PRINTER_INFO_REQUESTED,
+  PRINTER_PROVIDER_ON_PRINT_REQUESTED,
+  PROCESSES_ON_CREATED,
+  PROCESSES_ON_EXITED,
+  PROCESSES_ON_UNRESPONSIVE,
+  PROCESSES_ON_UPDATED,
+  PROCESSES_ON_UPDATED_WITH_MEMORY,
+  PROXY_ON_PROXY_ERROR,
+  RUNTIME_ON_BROWSER_UPDATE_AVAILABLE,
+  RUNTIME_ON_CONNECT,
+  RUNTIME_ON_CONNECT_EXTERNAL,
+  RUNTIME_ON_INSTALLED,
+  RUNTIME_ON_MESSAGE,
+  RUNTIME_ON_MESSAGE_EXTERNAL,
+  RUNTIME_ON_RESTART_REQUIRED,
+  RUNTIME_ON_STARTUP,
+  RUNTIME_ON_SUSPEND,
+  RUNTIME_ON_SUSPEND_CANCELED,
+  RUNTIME_ON_UPDATE_AVAILABLE,
+  SEARCH_ENGINES_PRIVATE_ON_SEARCH_ENGINES_CHANGED,
+  SERIAL_ON_RECEIVE,
+  SERIAL_ON_RECEIVE_ERROR,
+  SESSIONS_ON_CHANGED,
+  SETTINGS_PRIVATE_ON_PREFS_CHANGED,
+  SIGNED_IN_DEVICES_ON_DEVICE_INFO_CHANGE,
+  SOCKETS_TCP_ON_RECEIVE,
+  SOCKETS_TCP_ON_RECEIVE_ERROR,
+  SOCKETS_TCP_SERVER_ON_ACCEPT,
+  SOCKETS_TCP_SERVER_ON_ACCEPT_ERROR,
+  SOCKETS_UDP_ON_RECEIVE,
+  SOCKETS_UDP_ON_RECEIVE_ERROR,
+  STORAGE_ON_CHANGED,
+  STREAMS_PRIVATE_ON_EXECUTE_MIME_TYPE_HANDLER,
+  SYNC_FILE_SYSTEM_ON_FILE_STATUS_CHANGED,
+  SYNC_FILE_SYSTEM_ON_SERVICE_STATUS_CHANGED,
+  SYSTEM_DISPLAY_ON_DISPLAY_CHANGED,
+  SYSTEM_INDICATOR_ON_CLICKED,
+  SYSTEM_PRIVATE_ON_BRIGHTNESS_CHANGED,
+  SYSTEM_PRIVATE_ON_SCREEN_UNLOCKED,
+  SYSTEM_PRIVATE_ON_VOLUME_CHANGED,
+  SYSTEM_PRIVATE_ON_WOKE_UP,
+  SYSTEM_STORAGE_ON_ATTACHED,
+  SYSTEM_STORAGE_ON_DETACHED,
+  TAB_CAPTURE_ON_STATUS_CHANGED,
+  TABS_ON_ACTIVATED,
+  TABS_ON_ACTIVE_CHANGED,
+  TABS_ON_ATTACHED,
+  TABS_ON_CREATED,
+  TABS_ON_DETACHED,
+  TABS_ON_HIGHLIGHT_CHANGED,
+  TABS_ON_HIGHLIGHTED,
+  TABS_ON_MOVED,
+  TABS_ON_REMOVED,
+  TABS_ON_REPLACED,
+  TABS_ON_SELECTION_CHANGED,
+  TABS_ON_UPDATED,
+  TABS_ON_ZOOM_CHANGE,
+  TERMINAL_PRIVATE_ON_PROCESS_OUTPUT,
+  TEST_ON_MESSAGE,
+  TTS_ENGINE_ON_PAUSE,
+  TTS_ENGINE_ON_RESUME,
+  TTS_ENGINE_ON_SPEAK,
+  TTS_ENGINE_ON_STOP,
+  USB_ON_DEVICE_ADDED,
+  USB_ON_DEVICE_REMOVED,
+  VIRTUAL_KEYBOARD_PRIVATE_ON_BOUNDS_CHANGED,
+  VIRTUAL_KEYBOARD_PRIVATE_ON_TEXT_INPUT_BOX_FOCUSED,
+  VPN_PROVIDER_ON_CONFIG_CREATED,
+  VPN_PROVIDER_ON_CONFIG_REMOVED,
+  VPN_PROVIDER_ON_PACKET_RECEIVED,
+  VPN_PROVIDER_ON_PLATFORM_MESSAGE,
+  VPN_PROVIDER_ON_UIEVENT,
+  WALLPAPER_PRIVATE_ON_WALLPAPER_CHANGED_BY3RD_PARTY,
+  WEB_NAVIGATION_ON_BEFORE_NAVIGATE,
+  WEB_NAVIGATION_ON_COMMITTED,
+  WEB_NAVIGATION_ON_COMPLETED,
+  WEB_NAVIGATION_ON_CREATED_NAVIGATION_TARGET,
+  WEB_NAVIGATION_ON_DOMCONTENT_LOADED,
+  WEB_NAVIGATION_ON_ERROR_OCCURRED,
+  WEB_NAVIGATION_ON_HISTORY_STATE_UPDATED,
+  WEB_NAVIGATION_ON_REFERENCE_FRAGMENT_UPDATED,
+  WEB_NAVIGATION_ON_TAB_REPLACED,
+  WEB_REQUEST_ON_AUTH_REQUIRED,
+  WEB_REQUEST_ON_BEFORE_REDIRECT,
+  WEB_REQUEST_ON_BEFORE_REQUEST,
+  WEB_REQUEST_ON_BEFORE_SEND_HEADERS,
+  WEB_REQUEST_ON_COMPLETED,
+  WEB_REQUEST_ON_ERROR_OCCURRED,
+  WEB_REQUEST_ON_HEADERS_RECEIVED,
+  WEB_REQUEST_ON_RESPONSE_STARTED,
+  WEB_REQUEST_ON_SEND_HEADERS,
+  WEBRTC_AUDIO_PRIVATE_ON_SINKS_CHANGED,
+  WEBSTORE_ON_DOWNLOAD_PROGRESS,
+  WEBSTORE_ON_INSTALL_STAGE_CHANGED,
+  WEBSTORE_WIDGET_PRIVATE_ON_SHOW_WIDGET,
+  WEBVIEW_TAG_CLOSE,
+  WEBVIEW_TAG_CONSOLEMESSAGE,
+  WEBVIEW_TAG_CONTENTLOAD,
+  WEBVIEW_TAG_DIALOG,
+  WEBVIEW_TAG_EXIT,
+  WEBVIEW_TAG_FINDUPDATE,
+  WEBVIEW_TAG_LOADABORT,
+  WEBVIEW_TAG_LOADCOMMIT,
+  WEBVIEW_TAG_LOADREDIRECT,
+  WEBVIEW_TAG_LOADSTART,
+  WEBVIEW_TAG_LOADSTOP,
+  WEBVIEW_TAG_NEWWINDOW,
+  WEBVIEW_TAG_PERMISSIONREQUEST,
+  WEBVIEW_TAG_RESPONSIVE,
+  WEBVIEW_TAG_SIZECHANGED,
+  WEBVIEW_TAG_UNRESPONSIVE,
+  WEBVIEW_TAG_ZOOMCHANGE,
+  WINDOWS_ON_CREATED,
+  WINDOWS_ON_FOCUS_CHANGED,
+  WINDOWS_ON_REMOVED,
+  // Last entry: Add new entries above and ensure to update
+  // tools/metrics/histograms/histograms.xml.

[Ilya Sherman, 2015/06/23 21:34:20]

Please mention the script that automates this update.  Also, people seem to
frequently miss this comment in the other file.  Perhaps we could accentuate it
somehow?

[not at google - send to devlin, 2015/06/23 23:27:09]

Good point there should be a comment. Updated other file as well.

+  ENUM_BOUNDARY
+};
+
+}  // namespace events
+}  // namespace extensions
+
+#endif  // EXTENSIONS_BROWSER_EXTENSION_EVENT_HISTOGRAM_VALUE_H_