Bug 1821733 - Add chrome-only method for ending a wheel event group. r=smaug

Add a chrome-only method for ending a wheel event group. This can then
be used by the webdriver to ensure that the wheel event group does not
live longer than the action chain.

Differential Revision: https://phabricator.services.mozilla.com/D177923

dom/base/ChromeUtils.cpp

@@ -52,6 +52,7 @@
 #include "mozilla/ipc/UtilityProcessManager.h"
 #include "mozilla/ipc/UtilityProcessHost.h"
 #include "mozilla/net/UrlClassifierFeatureFactory.h"
+#include "mozilla/WheelHandlingHelper.h"
 #include "IOActivityMonitor.h"
 #include "nsNativeTheme.h"
 #include "nsThreadUtils.h"
@@ -1696,6 +1697,15 @@ void ChromeUtils::ResetLastExternalProtocolIframeAllowed(
   PopupBlocker::ResetLastExternalProtocolIframeAllowed();
 }
 
+/* static */
+void ChromeUtils::EndWheelTransaction(GlobalObject& aGlobal) {
+  // This allows us to end the current wheel transaction from the browser
+  // chrome. We do not need to perform any checks before calling
+  // EndTransaction(), as it should do nothing in the case that there is
+  // no current wheel transaction.
+  WheelTransaction::EndTransaction();
+}
+
 /* static */
 void ChromeUtils::RegisterWindowActor(const GlobalObject& aGlobal,
                                       const nsACString& aName,