[NFC] Only connect to NFC impl if ExecutionContext supports it

third_party/WebKit/Source/modules/nfc/NFC.h

 // 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.
 
 #ifndef NFC_h
 #define NFC_h
 
 #include "bindings/core/v8/ScriptPromise.h"
 #include "bindings/modules/v8/StringOrArrayBufferOrNFCMessage.h"
 #include "core/dom/ContextLifecycleObserver.h"
@@ skipping 47 matching lines @@
   // Cancels all watch operations.
   ScriptPromise cancelWatch(ScriptState*);
 
   // Implementation of PageVisibilityObserver.
   void PageVisibilityChanged() override;
 
   // Interface required by garbage collection.
   DECLARE_VIRTUAL_TRACE();
 
  private:
+  // Returns boolean indicating whether NFC is supported in |context|. If not,
+  // |error_message| gives a message indicating why not.
+  bool IsSupportedInContext(ExecutionContext*, String&);

[jochen (gone - plz use gerrit), 2017/05/15 05:34:55]

nit. should be String& error_message, as it's not obvious what that parameter is
otherwise

[blundell, 2017/05/15 07:27:55]

Done.

+
   // Returns promise with DOMException if feature is not supported
   // or when context is not secure. Otherwise, returns empty promise.
   ScriptPromise RejectIfNotSupported(ScriptState*);
 
   void OnRequestCompleted(ScriptPromiseResolver*,
                           device::nfc::mojom::blink::NFCErrorPtr);
   void OnConnectionError();
   void OnWatchRegistered(MessageCallback*,
                          ScriptPromiseResolver*,
                          uint32_t id,
                          device::nfc::mojom::blink::NFCErrorPtr);
 
   // device::nfc::mojom::blink::NFCClient implementation.
   void OnWatch(const WTF::Vector<uint32_t>& ids,
                device::nfc::mojom::blink::NFCMessagePtr) override;
 
  private:
   explicit NFC(LocalFrame*);
   device::nfc::mojom::blink::NFCPtr nfc_;
   mojo::Binding<device::nfc::mojom::blink::NFCClient> client_;
   HeapHashSet<Member<ScriptPromiseResolver>> requests_;
   using WatchCallbacksMap = HeapHashMap<uint32_t, Member<MessageCallback>>;
   WatchCallbacksMap callbacks_;
 };
 
 }  // namespace blink
 
 #endif  // NFC_h