[webnfc] Remove unused mWatcherId in NfcImpl.java

Bug: 520391
Change-Id: I3c687f7af552434f0050ae4216b70b27cf06d010
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2143654Reviewed-by: Rijubrata Bhaumik <rijubrata.bhaumik@intel.com>
Commit-Queue: Donna Wu <donna.wu@intel.com>
Cr-Commit-Position: refs/heads/master@{#758762}

services/device/nfc/android/java/src/org/chromium/device/nfc/NfcImpl.java

@@ -99,11 +99,6 @@ public class NfcImpl implements Nfc {
      */
     private NfcClient mClient;
 
-    /**
-     * Watcher id that is incremented for each #watch call.
-     */
-    private int mWatcherId;
-
     /**
      * Map of watchId <-> NdefScanOptions. All NdefScanOptions are matched against tag that is in
      * proximity, when match algorithm (@see #matchesWatchOptions) returns true, watcher with
@@ -245,6 +240,7 @@ public class NfcImpl implements Nfc {
      * @see NfcClient#onWatch(int[] id, String serial_number, NdefMessage message)
      *
      * @param options used to filter NdefMessages, @see NdefScanOptions.
+     * @param id request ID from Blink which will be the watch ID if succeeded.
      * @param callback that is used to notify caller when watch() is completed.
      */
     @Override