[webnfc] Implement nfc.watch in blink nfc module.

device/nfc/nfc.mojom

 // 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.
 
 module device.nfc;
 
 enum NFCErrorType {
   SECURITY,
   NOT_SUPPORTED,
   DEVICE_DISABLED,
@@ skipping 47 matching lines @@
 };
 
 struct NFCMessage {
   // The body of the NFCMessage is a collection of NFCRecord objects.
   array<NFCRecord> data;
 
   // The |url| field is an ASCII serialized origin, optionally followed by a URL
   // path. It represents Web NFC id, that can be used for matching Web NFC
   // content with the filter specified by |url| field in NFCWatchOptions.
   string? url;
+
+  // Maximum size of NFC message that can be sent over IPC is 32KB.
+  const uint32 kMaxNFCMessageSize = 32768;

[dcheng, 2016/09/08 04:42:38]

Nit: omit NFCMessage here, since the constant is embedded in a struct called
NFCMessage.

[shalamov, 2016/09/22 13:53:22]

Done.

 };
 
 struct NFCPushOptions {
   // The target of the push operation.
   NFCPushTarget target;
 
   // The timeout for the push operation, in milliseconds.
   double timeout;
 
   // If the property is true, the push operation will suspend active watchers
@@ skipping 47 matching lines @@
   // visibility or focus is lost.
   SuspendNFCOperations();
 
   // Resumes all suspended NFC operations.
   ResumeNFCOperations();
 };
 
 interface NFCClient {
   OnWatch(array<uint32> watch_ids, NFCMessage message);
 };