[webnfc] Implement push() method in blink nfc module.

device/nfc/nfc.mojom

Index: device/nfc/nfc.mojom
diff --git a/device/nfc/nfc.mojom b/device/nfc/nfc.mojom
index 6ba8b7a1ad72449bed2c27c18dc09fdfdc902f4f..e062adadc3752f9072f29688b54b5c69838aa143 100644
--- a/device/nfc/nfc.mojom
+++ b/device/nfc/nfc.mojom
@@ -68,16 +68,33 @@ struct NFCWatchOptions {
 };
 
 interface NFC {
-  SetClient(NFCClient client);
+  // Pushes data to NFC device.
+  // NFCPushOptions specify timeout and type of device where data should be
+  // pushed. If timeout is defined and data is not pushed before timeout is
+  // expired, callback with corresponding error is called.
   Push(NFCMessage message, NFCPushOptions? options) => (NFCError? error);
+
+  // Cancels pending push request.
   CancelPush(NFCPushTarget target) => (NFCError? error);
+
+  // Starts watching for nearby NFC devices with data that matches
+  // NFCWatchOptions filtering criteria. On success, watch ID is returned.
   Watch(NFCWatchOptions options) => (uint32 id, NFCError? error);
+
+  // Cancels watch operation with provided id.
   CancelWatch (uint32 id) => (NFCError? error);
+
+  // Cancels all watch operations.
   CancelAllWatches () => (NFCError? error);
+
+  // Subscribes to watch events. If multiple watch operations match discovered
+  // NFCMessage, callback is called with array of matched watch IDs.
+  SubscribeToWatchEvents() => (array<uint32> watchIDs, NFCMessage message);
+
+  // Suspends all pending NFC operations. Could be used when web page
+  // visibility or focus is lost.
   SuspendNFCOperations();
-  ResumeNFCOperations();
-};
 
-interface NFCClient {
-  OnWatch(uint32 id, NFCMessage message);
+  // Resumes all suspended NFC operations.
+  ResumeNFCOperations();
 };