Only show a beforeunload dialog if a frame has been interacted with.

third_party/WebKit/Source/core/dom/Document.cpp

Index: third_party/WebKit/Source/core/dom/Document.cpp
diff --git a/third_party/WebKit/Source/core/dom/Document.cpp b/third_party/WebKit/Source/core/dom/Document.cpp
index 43aaf0a8818e7d3dffa5b297bf1756910e408cac..70079aa2cfe24758ac5aebdb69026add88d0fe90 100644
--- a/third_party/WebKit/Source/core/dom/Document.cpp
+++ b/third_party/WebKit/Source/core/dom/Document.cpp
@@ -3055,6 +3055,14 @@ bool Document::dispatchBeforeUnloadEvent(ChromeClient& chromeClient,
   if (!frame() || beforeUnloadEvent->returnValue().isNull())
     return true;
 
+  if (!frame()->hasReceivedUserGesture()) {
+    addConsoleMessage(ConsoleMessage::create(
+        JSMessageSource, ErrorMessageLevel,
+        "Blocked attempt to show a 'beforeunload' confirmation panel for a "
+        "frame without a user gesture."));
+    return true;
+  }
+
   if (didAllowNavigation) {
     addConsoleMessage(ConsoleMessage::create(
         JSMessageSource, ErrorMessageLevel,