Add IDL and initial Blink API for Background Sync

Source/modules/modules.gypi

 {
   'includes': [
     '../core/core_generated.gypi',
     'modules_generated.gypi',
   ],
   'variables': {
     # Experimental hooks for embedder to provide extra IDL and source files.
     #
     # Note: this is not a supported API. If you rely on this, you will be broken
     # from time to time as the code generator changes in backward incompatible
     # ways.
     'extra_blink_module_idl_files': [],
     'extra_blink_module_files': [],
     # Files for which bindings (.cpp and .h files) will be generated
     'modules_idl_files': [
       '<@(extra_blink_module_idl_files)',
+      'background_sync/SyncEvent.idl',
+      'background_sync/SyncManager.idl',
+      'background_sync/SyncRegistration.idl',
       'battery/BatteryManager.idl',
       'bluetooth/Bluetooth.idl',
       'bluetooth/BluetoothDevice.idl',
       'bluetooth/BluetoothDiscovery.idl',
       'credentialmanager/Credential.idl',
       'credentialmanager/CredentialsContainer.idl',
       'credentialmanager/FederatedCredential.idl',
       'credentialmanager/LocalCredential.idl',
       'crypto/Crypto.idl',
       'crypto/CryptoKey.idl',
@@ skipping 185 matching lines @@
       'webmidi/MIDIMessageEvent.idl',
       'webmidi/MIDIOutput.idl',
       'webmidi/MIDIOutputMap.idl',
       'webmidi/MIDIPort.idl',
       'webmidi/MIDISuccessCallback.idl',
       'websockets/CloseEvent.idl',
       'websockets/WebSocket.idl',
     ],
     # 'partial interface' or target (right side of) 'implements'
     'modules_dependency_idl_files': [
+      'background_sync/ServiceWorkerGlobalScopeSync.idl',
+      'background_sync/ServiceWorkerRegistrationSync.idl',
       'battery/NavigatorBattery.idl',
       'beacon/NavigatorBeacon.idl',
       'bluetooth/NavigatorBluetooth.idl',
       'credentialmanager/NavigatorCredentials.idl',
       'crypto/WindowCrypto.idl',
       'crypto/WorkerGlobalScopeCrypto.idl',
       'device_light/WindowDeviceLight.idl',
       'device_orientation/WindowDeviceMotion.idl',
       'device_orientation/WindowDeviceOrientation.idl',
       'donottrack/NavigatorDoNotTrack.idl',
@@ skipping 37 matching lines @@
       'serviceworkers/NavigatorServiceWorker.idl',
       'speech/WindowSpeech.idl',
       'speech/WindowSpeechSynthesis.idl',
       'vibration/NavigatorVibration.idl',
       'webaudio/WindowWebAudio.idl',
       'webdatabase/WindowWebDatabase.idl',
       'webmidi/NavigatorWebMIDI.idl',
     ],
     # interfaces that inherit from Event
     'modules_event_idl_files': [
+      'background_sync/SyncEvent.idl',
       'device_light/DeviceLightEvent.idl',
       'device_orientation/DeviceMotionEvent.idl',
       'device_orientation/DeviceOrientationEvent.idl',
       'encryptedmedia/MediaEncryptedEvent.idl',
       'encryptedmedia/MediaKeyMessageEvent.idl',
       'gamepad/GamepadEvent.idl',
       'geofencing/GeofencingEvent.idl',
       'indexeddb/IDBVersionChangeEvent.idl',
       'mediastream/MediaStreamEvent.idl',
       'mediastream/MediaStreamTrackEvent.idl',
@@ skipping 10 matching lines @@
       'speech/SpeechRecognitionError.idl',
       'speech/SpeechRecognitionEvent.idl',
       'speech/SpeechSynthesisEvent.idl',
       'webaudio/AudioProcessingEvent.idl',
       'webaudio/OfflineAudioCompletionEvent.idl',
       'webmidi/MIDIConnectionEvent.idl',
       'webmidi/MIDIMessageEvent.idl',
       'websockets/CloseEvent.idl',
     ],
     'modules_dictionary_idl_files': [
+      'background_sync/SyncEventInit.idl',
+      'background_sync/SyncRegistrationOptions.idl',
       'device_light/DeviceLightEventInit.idl',
       'encoding/TextDecodeOptions.idl',
       'encoding/TextDecoderOptions.idl',
       'encryptedmedia/MediaEncryptedEventInit.idl',
       'encryptedmedia/MediaKeyMessageEventInit.idl',
       'encryptedmedia/MediaKeySystemConfiguration.idl',
       'encryptedmedia/MediaKeySystemMediaCapability.idl',
       'filesystem/FileSystemFlags.idl',
       'gamepad/GamepadEventInit.idl',
       'geofencing/CircularGeofencingRegionInit.idl',
@@ skipping 26 matching lines @@
       '<(blink_modules_output_dir)/EventModules.cpp',
       '<(blink_modules_output_dir)/EventModulesHeaders.h',
       '<(blink_modules_output_dir)/EventModulesNames.cpp',
       '<(blink_modules_output_dir)/EventModulesNames.h',
       '<(blink_modules_output_dir)/EventTargetModulesNames.cpp',
       '<(blink_modules_output_dir)/EventTargetModulesNames.h',
       '<(blink_modules_output_dir)/IndexedDBNames.cpp',
       '<(blink_modules_output_dir)/IndexedDBNames.h',
     ],
     'generated_modules_dictionary_files': [
+      '<(blink_modules_output_dir)/background_sync/SyncEventInit.cpp',
+      '<(blink_modules_output_dir)/background_sync/SyncEventInit.h',
+      '<(blink_modules_output_dir)/background_sync/SyncRegistrationOptions.cpp',
+      '<(blink_modules_output_dir)/background_sync/SyncRegistrationOptions.h',
       '<(blink_modules_output_dir)/device_light/DeviceLightEventInit.cpp',
       '<(blink_modules_output_dir)/device_light/DeviceLightEventInit.h',
       '<(blink_modules_output_dir)/encoding/TextDecodeOptions.cpp',
       '<(blink_modules_output_dir)/encoding/TextDecodeOptions.h',
       '<(blink_modules_output_dir)/encoding/TextDecoderOptions.cpp',
       '<(blink_modules_output_dir)/encoding/TextDecoderOptions.h',
       '<(blink_modules_output_dir)/encryptedmedia/MediaEncryptedEventInit.cpp',
       '<(blink_modules_output_dir)/encryptedmedia/MediaEncryptedEventInit.h',
       '<(blink_modules_output_dir)/encryptedmedia/MediaKeyMessageEventInit.cpp',
       '<(blink_modules_output_dir)/encryptedmedia/MediaKeyMessageEventInit.h',
@@ skipping 111 matching lines @@
       'accessibility/AXTableCell.cpp',
       'accessibility/AXTableCell.h',
       'accessibility/AXTableColumn.cpp',
       'accessibility/AXTableColumn.h',
       'accessibility/AXTableHeaderContainer.cpp',
       'accessibility/AXTableHeaderContainer.h',
       'accessibility/AXTableRow.cpp',
       'accessibility/AXTableRow.h',
       'accessibility/InspectorAccessibilityAgent.cpp',
       'accessibility/InspectorAccessibilityAgent.h',
+      'background_sync/ServiceWorkerGlobalScopeSync.h',
+      'background_sync/ServiceWorkerRegistrationSync.cpp',
+      'background_sync/ServiceWorkerRegistrationSync.h',
+      'background_sync/SyncError.cpp',
+      'background_sync/SyncError.h',
+      'background_sync/SyncEvent.cpp',
+      'background_sync/SyncEvent.h',
+      'background_sync/SyncManager.cpp',
+      'background_sync/SyncManager.h',
+      'background_sync/SyncRegistration.cpp',
+      'background_sync/SyncRegistration.h',
+      'background_sync/SyncRegistrationCallbacks.cpp',
+      'background_sync/SyncRegistrationCallbacks.h',
       'battery/BatteryDispatcher.cpp',
       'battery/BatteryDispatcher.h',
       'battery/BatteryManager.cpp',
       'battery/BatteryManager.h',
       'battery/BatteryStatus.cpp',
       'battery/BatteryStatus.h',
       'battery/NavigatorBattery.cpp',
       'battery/NavigatorBattery.h',
       'beacon/NavigatorBeacon.cpp',
       'beacon/NavigatorBeacon.h',
@@ skipping 743 matching lines @@
       'indexeddb/IDBKeyPathTest.cpp',
       'indexeddb/IDBRequestTest.cpp',
       'indexeddb/IDBTransactionTest.cpp',
       'serviceworkers/CacheTest.cpp',
       'serviceworkers/ServiceWorkerContainerTest.cpp',
       'websockets/DOMWebSocketTest.cpp',
       'websockets/DocumentWebSocketChannelTest.cpp',
     ],
   },
 }