Presentation API: PresentationRequest.start() requires user gesture.

Source/modules/presentation/PresentationRequest.cpp

Index: Source/modules/presentation/PresentationRequest.cpp
diff --git a/Source/modules/presentation/PresentationRequest.cpp b/Source/modules/presentation/PresentationRequest.cpp
index 63f8aa2b4bbeda17b2af28b4d2738fad84e4dbfb..04b209a8cd634a693adddfb955c5ec1123727b60 100644
--- a/Source/modules/presentation/PresentationRequest.cpp
+++ b/Source/modules/presentation/PresentationRequest.cpp
@@ -19,6 +19,7 @@
 #include "modules/presentation/PresentationError.h"
 #include "modules/presentation/PresentationSession.h"
 #include "modules/presentation/PresentationSessionCallbacks.h"
+#include "platform/UserGestureIndicator.h"
 
 namespace blink {
 
@@ -82,6 +83,11 @@ ScriptPromise PresentationRequest::start(ScriptState* scriptState)
     ScriptPromiseResolver* resolver = ScriptPromiseResolver::create(scriptState);
     ScriptPromise promise = resolver->promise();
 
+    if (!UserGestureIndicator::processingUserGesture()) {
+        resolver->reject(DOMException::create(InvalidAccessError, "PresentationRequest::start() requires user gesture."));
+        return promise;
+    }
+
     WebPresentationClient* client = presentationClient(executionContext());
     if (!client) {
         resolver->reject(DOMException::create(InvalidStateError, "The PresentationRequest is no longer associated to a frame."));