Cherry-pick 275229@main (c67d585). https://bugs.webkit.org/show_bug.c…

…gi?id=269951

    Pause control does not work in in-window mode
    https://bugs.webkit.org/show_bug.cgi?id=269951
    rdar://122834226

    Reviewed by Jer Noble.

    This bug was caused by both our event handler for clicking on the pause button
    and youtube's event handler for clicking on the video both being activated,
    causing the video to pause and then immediately be played again. To prevent
    this, in our button's event handler we now call stopPropagation().

    * Source/WebCore/Modules/modern-media-controls/controls/button.js:
    (Button.prototype.handleEvent):

    Canonical link: https://commits.webkit.org/275229@main

Canonical link: https://commits.webkit.org/274313.182@webkitglib/2.44

Source/WebCore/Modules/modern-media-controls/controls/button.js

@@ -150,6 +150,7 @@ class Button extends LayoutItem
 
     handleEvent(event)
     {
+        event.stopPropagation();
         if (event.target === this._imageSource) {
             if (event.type === "load")
                 this._imageSourceDidLoad();