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

Source/core/rendering/RenderLayer.cpp

Index: Source/core/rendering/RenderLayer.cpp
diff --git a/Source/core/rendering/RenderLayer.cpp b/Source/core/rendering/RenderLayer.cpp
index 7387c163b2cee440c9f12ad25e9cf0133bc86707..6ae6fb18c1559d7092ee9cebe7aa294d0478d295 100644
--- a/Source/core/rendering/RenderLayer.cpp
+++ b/Source/core/rendering/RenderLayer.cpp
@@ -2404,7 +2404,10 @@ bool RenderLayer::hitTest(const HitTestRequest& request, const HitTestLocation&
         // 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;
         }