Ignore fullscreen requests for the current fullscreen element

Source/core/dom/Fullscreen.cpp

Index: Source/core/dom/Fullscreen.cpp
diff --git a/Source/core/dom/Fullscreen.cpp b/Source/core/dom/Fullscreen.cpp
index e2e2d61085182817d15215f6af7ce1fb03380930..327f05a12c15849a3b42d4230f4fc8e751a1edb9 100644
--- a/Source/core/dom/Fullscreen.cpp
+++ b/Source/core/dom/Fullscreen.cpp
@@ -207,6 +207,10 @@ void Fullscreen::requestFullscreen(Element& element, RequestType requestType)
     if (!document()->isActive())
         return;
 
+    // If |element| is on top of |doc|'s fullscreen element stack, terminate these substeps.
+    if (&element == fullscreenElement())
+        return;
+
     do {
         // 1. If any of the following conditions are true, terminate these steps and queue a task to fire
         // an event named fullscreenerror with its bubbles attribute set to true on the context object's