Enable WebUSB through the Experimental Framework.

third_party/WebKit/LayoutTests/virtual/stable/webexposed/global-interface-listing-expected.txt

 CONSOLE WARNING: 'webkitOfflineAudioContext' is deprecated. Please use 'OfflineAudioContext' instead.
 CONSOLE WARNING: 'webkitAudioContext' is deprecated. Please use 'AudioContext' instead.
 CONSOLE WARNING: 'window.webkitStorageInfo' is deprecated. Please use 'navigator.webkitTemporaryStorage' or 'navigator.webkitPersistentStorage' instead.
 CONSOLE WARNING: 'webkitIDBTransaction' is deprecated. Please use 'IDBTransaction' instead.
 CONSOLE WARNING: 'webkitIDBRequest' is deprecated. Please use 'IDBRequest' instead.
 CONSOLE WARNING: 'webkitIDBObjectStore' is deprecated. Please use 'IDBObjectStore' instead.
 CONSOLE WARNING: 'webkitIDBKeyRange' is deprecated. Please use 'IDBKeyRange' instead.
 CONSOLE WARNING: 'webkitIDBIndex' is deprecated. Please use 'IDBIndex' instead.
 CONSOLE WARNING: 'webkitIDBFactory' is deprecated. Please use 'IDBFactory' instead.
 CONSOLE WARNING: 'webkitIDBDatabase' is deprecated. Please use 'IDBDatabase' instead.
 CONSOLE WARNING: 'webkitIDBCursor' is deprecated. Please use 'IDBCursor' instead.
 CONSOLE WARNING: 'webkitIndexedDB' is deprecated. Please use 'indexedDB' instead.
+CONSOLE ERROR: The 'WebUSB' feature is currently enabled in limited trials. Please see [Phosphor console URL] for information on enabling a trial for your site.
 CONSOLE ERROR: The 'WebBluetooth' feature is currently enabled in limited trials. Please see [Phosphor console URL] for information on enabling a trial for your site.
 CONSOLE WARNING: 'webkitURL' is deprecated. Please use 'URL' instead.
 This test documents all interface attributes and methods on the global window object and element instances.
 
 On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE".
 
 
 [INTERFACES]
 interface AnalyserNode : AudioNode
     attribute @@toStringTag
@@ skipping 3320 matching lines @@
     getter mediaDevices
     getter mimeTypes
     getter onLine
     getter permissions
     getter platform
     getter plugins
     getter presentation
     getter product
     getter productSub
     getter serviceWorker
+    getter usb
     getter userAgent
     getter vendor
     getter vendorSub
     getter webkitPersistentStorage
     getter webkitTemporaryStorage
     method constructor
     method getBattery
     method getGamepads
     method javaEnabled
     method registerProtocolHandler
@@ skipping 3057 matching lines @@
     setter username
 [GLOBAL OBJECT]
     attribute BluetoothAdvertisingData
     attribute BluetoothCharacteristicProperties
     attribute BluetoothDevice
     attribute BluetoothRemoteGATTCharacteristic
     attribute BluetoothRemoteGATTServer
     attribute BluetoothRemoteGATTService
     attribute BluetoothUUID
     attribute GCController
+    attribute USBAlternateInterface
+    attribute USBConfiguration
+    attribute USBConnectionEvent
+    attribute USBDevice
+    attribute USBEndpoint
+    attribute USBInTransferResult
+    attribute USBInterface
+    attribute USBIsochronousInTransferPacket
+    attribute USBIsochronousInTransferResult
+    attribute USBIsochronousOutTransferPacket
+    attribute USBIsochronousOutTransferResult
+    attribute USBOutTransferResult
     attribute accessibilityController
     attribute applicationCache
     attribute caches
     attribute clientInformation
     attribute closed
     attribute console
     attribute crypto
     attribute defaultStatus
     attribute defaultstatus
     attribute devicePixelRatio
@@ skipping 178 matching lines @@
     method stop
     method webkitCancelAnimationFrame
     method webkitCancelRequestAnimationFrame
     method webkitRequestAnimationFrame
     method webkitRequestFileSystem
     method webkitResolveLocalFileSystemURL
 PASS successfullyParsed is true
 
 TEST COMPLETE