[DevTools] Account for synthetic events in deepElementFromPoint()

third_party/WebKit/Source/devtools/front_end/ui/GlassPane.js

Index: third_party/WebKit/Source/devtools/front_end/ui/GlassPane.js
diff --git a/third_party/WebKit/Source/devtools/front_end/ui/GlassPane.js b/third_party/WebKit/Source/devtools/front_end/ui/GlassPane.js
index 831020febb1ea1fd6b2f977786e205be74dfe925..82664a70d951cd7c9bf2b675bf6702bcb3542ffe 100644
--- a/third_party/WebKit/Source/devtools/front_end/ui/GlassPane.js
+++ b/third_party/WebKit/Source/devtools/front_end/ui/GlassPane.js
@@ -143,7 +143,8 @@ UI.GlassPane = class {
   _onMouseDown(event) {
     if (!this._onClickOutsideCallback)
       return;
-    if (this.contentElement.isSelfOrAncestor(/** @type {?Node} */ (event.deepElementFromPoint())))
+    var node = event.deepElementFromPoint();
+    if (!node || this.contentElement.isSelfOrAncestor(node))
       return;
     this._onClickOutsideCallback.call(null, event);
   }