Change mojo enums to be scoped enums in the generated C++ bindings.

Some mojo enums were previously not proper enums: they were constants
for bitfields. These have been replaced by const int32s in the mojoms:
- mus.mojom.EventFlags
- mus.mojom.MouseEventFlags
- mus.mojom.ResizeBehavior
- mus.mojom.WindowTree.AccessPolicy

Some mojo enum values now conflict with macros (mostly on Windows) and
needed to change:
- mus.mojom.Cursor.NULL became CURSOR_NULL (again)
- mus.mojom.KeyboardCode.DELETE became DELETE_KEY
- mus.mojom.WindowManagerErrorCode.ERROR_ACCESS_DENIED became
  ACCESS_DENIED
- device.usb.TransferDirection.IN became INBOUND
- device.usb.TransferDirection.OUT became OUTBOUND
- device.usb.TransferStatus.ERROR became TRANSFER_ERROR
- device.NFCRecordType.OPAQUE became OPAQUE_RECORD
- media.interfaces.Decryptor.Status.ERROR became DECRYPTION_ERROR
- skia.AlphaType.OPAQUE became ALPHA_TYPE_OPAQUE

Review URL: https://codereview.chromium.org/1527183003

Cr-Commit-Position: refs/heads/master@{#370632}
198 files changed