[WebNFC] Notify client once when error happens

Instead of calling `mClient.onError(error)` as many times as the number
of watchers, this CL makes sure we only call it once as the client takes
care of dispatching to all readers.

Bug: 520391
Change-Id: I82f2cf985d86e824c8a8cb9cbec85b7016334484
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2557018Reviewed-by: Rijubrata Bhaumik <rijubrata.bhaumik@intel.com>
Reviewed-by: Reilly Grant <reillyg@chromium.org>
Commit-Queue: François Beaufort <beaufort.francois@gmail.com>
Cr-Commit-Position: refs/heads/master@{#832234}

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

@@ -560,9 +560,7 @@ public class NfcImpl implements Nfc {
      * Notify all active watchers that an error happened when trying to read the tag coming nearby.
      */
     private void notifyErrorToAllWatchers(NdefError error) {
-        for (int i = 0; i < mWatchIds.size(); i++) {
-            mClient.onError(error);
-        }
+        if (mWatchIds.size() != 0) mClient.onError(error);
     }
 
     /**