Implement Middle Click Autoscroll on all platforms not just Windows

content/renderer/render_view_impl.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/renderer/render_view_impl.h"
 
 #include <algorithm>
 #include <cmath>
 #include <memory>
 
@@ skipping 1152 matching lines @@
   settings->setUseSolidColorScrollbars(prefs.use_solid_color_scrollbars);
 
   settings->setShowContextMenuOnMouseUp(prefs.context_menu_on_mouse_up);
   settings->setAlwaysShowContextMenuOnTouch(
       prefs.always_show_context_menu_on_touch);
 
 #if defined(OS_MACOSX)
   settings->setDoubleTapToZoomEnabled(true);
   web_view->setMaximumLegibleScale(prefs.default_maximum_page_scale_factor);
 #endif
+
+#if defined(OS_WIN)
+  WebRuntimeFeatures::enableMiddleClickAutoscroll(true);
+#endif
 }
 
 /*static*/
 RenderViewImpl* RenderViewImpl::Create(CompositorDependencies* compositor_deps,
                                        const ViewMsg_New_Params& params,
                                        bool was_created_by_renderer) {
   DCHECK(params.view_id != MSG_ROUTING_NONE);
   RenderViewImpl* render_view = NULL;
   if (g_create_render_view_impl)
     render_view = g_create_render_view_impl(compositor_deps, params);
@@ skipping 1866 matching lines @@
         return render_frame->focused_pepper_plugin();
     }
     frame = frame->traverseNext(false);
   }
 
   return nullptr;
 }
 #endif
 
 }  // namespace content