Avoid allocation during NFCReader::HasPendingActivity()

HasPendingActivity of classes inheriting from ScriptWrappable are
not allowed to allocate. Using GetNFCProxy in HasPendingActivity
resulted in allocation.
This issue was found by clusterfuzz.

Added a call to GetNFCProxy during NFCReader initialization.
This guarantees that a NFCProxy object exists when we call
HasPendingActivity down the line and avoids the allocation.

Bug: 1001974
Change-Id: I83abd54641618a56d33a73150ffdfccd3d64a73e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1796370
Commit-Queue: Omer Katz <omerkatz@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#695589}

third_party/blink/renderer/modules/nfc/nfc_reader.cc

@@ -26,7 +26,11 @@ NFCReader* NFCReader::Create(ExecutionContext* context) {
 }
 
 NFCReader::NFCReader(ExecutionContext* context)
-    : ContextLifecycleObserver(context) {}
+    : ContextLifecycleObserver(context) {
+  // Call GetNFCProxy to create a proxy. This guarantees no allocation will
+  // be needed when calling HasPendingActivity later during gc tracing.
+  GetNfcProxy();
+}
 
 NFCReader::~NFCReader() = default;