Mousemove event should be fired when the mouse stays in the document but there is no element.

Source/core/rendering/RenderLayer.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  *
  * Portions are Copyright (C) 1998 Netscape Communications Corporation.
  *
  * Other contributors:
  *   Robert O'Callahan <roc+@cs.cmu.edu>
  *   David Baron <dbaron@fas.harvard.edu>
  *   Christian Biesinger <cbiesinger@web.de>
  *   Randall Jesup <rjesup@wgate.com>
@@ skipping 2386 matching lines @@
 
     LayoutRect hitTestArea = renderer()->view()->documentRect();
     if (!request.ignoreClipping())
         hitTestArea.intersect(frameVisibleRect(renderer()));
 
     RenderLayer* insideLayer = hitTestLayer(this, 0, request, result, hitTestArea, hitTestLocation, false);
     if (!insideLayer) {
         // We didn't hit any layer. If we are the root layer and the mouse is -- or just was -- down,
         // return ourselves. We do this so mouse events continue getting delivered after a drag has
         // exited the WebView, and so hit testing over a scrollbar hits the content document.
-        if (!request.isChildFrameHitTest() && (request.active() || request.release()) && isRootLayer()) {
+        // In addtion, the mouse is possible to stay in document but there is no element.
+        // At that time, the events of the mouse should be fired. 
+        LayoutPoint hitPoint = hitTestLocation.point();
+        if (!request.isChildFrameHitTest() && ((request.active() || request.release()) || (request.move() && hitTestArea.contains(hitPoint.x(), hitPoint.y()))) && isRootLayer()) {
             renderer()->updateHitTestResult(result, toRenderView(renderer())->flipForWritingMode(hitTestLocation.point()));
             insideLayer = this;
         }
     }
 
     // Now determine if the result is inside an anchor - if the urlElement isn't already set.
     Node* node = result.innerNode();
     if (node && !result.URLElement())
         result.setURLElement(node->enclosingLinkEventParentOrSelf());
 
@@ skipping 1268 matching lines @@
     }
 }
 
 void showLayerTree(const blink::RenderObject* renderer)
 {
     if (!renderer)
         return;
     showLayerTree(renderer->enclosingLayer());
 }
 #endif