Implement Middle Click Autoscroll on all platforms not just Windows

third_party/WebKit/Source/web/WebRuntimeFeatures.cpp

Index: third_party/WebKit/Source/web/WebRuntimeFeatures.cpp
diff --git a/third_party/WebKit/Source/web/WebRuntimeFeatures.cpp b/third_party/WebKit/Source/web/WebRuntimeFeatures.cpp
index 80f5599061f8dbfe675d5115bb7609ef0a941360..d23570b0adebbcbc88130d3257536f8cbb11047f 100644
--- a/third_party/WebKit/Source/web/WebRuntimeFeatures.cpp
+++ b/third_party/WebKit/Source/web/WebRuntimeFeatures.cpp
@@ -205,6 +205,11 @@ void WebRuntimeFeatures::enablePagePopup(bool enable)
     RuntimeEnabledFeatures::setPagePopupEnabled(enable);
 }
 
+void WebRuntimeFeatures::enablePanScrolling(bool enable)
+{
+    RuntimeEnabledFeatures::setPanScrollingEnabled(enable);
+}
+
 void WebRuntimeFeatures::enableParseHTMLOnMainThread(bool enable)
 {
     RuntimeEnabledFeatures::setParseHTMLOnMainThreadEnabled(enable);