Implement Middle Click Autoscroll on all platforms not just Windows

third_party/WebKit/Source/web/WebRuntimeFeatures.cpp

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 187 matching lines @@
 bool WebRuntimeFeatures::isOriginTrialsEnabled()
 {
     return RuntimeEnabledFeatures::originTrialsEnabled();
 }
 
 void WebRuntimeFeatures::enablePagePopup(bool enable)
 {
     RuntimeEnabledFeatures::setPagePopupEnabled(enable);
 }
 
+void WebRuntimeFeatures::enablePanScrolling(bool enable)
+{
+    RuntimeEnabledFeatures::setPanScrollingEnabled(enable);
+}
+
 void WebRuntimeFeatures::enableParseHTMLOnMainThread(bool enable)
 {
     RuntimeEnabledFeatures::setParseHTMLOnMainThreadEnabled(enable);
 }
 
 void WebRuntimeFeatures::enablePassiveDocumentEventListeners(bool enable)
 {
     RuntimeEnabledFeatures::setPassiveDocumentEventListenersEnabled(enable);
 }
 
@@ skipping 166 matching lines @@
 {
     RuntimeEnabledFeatures::setTimerThrottlingForHiddenFramesEnabled(enable);
 }
 
 void WebRuntimeFeatures::enableSendBeaconThrowForBlobWithNonSimpleType(bool enable)
 {
     RuntimeEnabledFeatures::setSendBeaconThrowForBlobWithNonSimpleTypeEnabled(enable);
 }
 
 } // namespace blink