Scrollbar ThumbLength is not updated when window size is changed.

cc/layers/painted_scrollbar_layer.cc

Index: cc/layers/painted_scrollbar_layer.cc
diff --git a/cc/layers/painted_scrollbar_layer.cc b/cc/layers/painted_scrollbar_layer.cc
index c0b2a728e3c9077c46a7f194dce94174d0780fd0..7062bc1e9bade7910cde353e5be9697cd9922e80 100644
--- a/cc/layers/painted_scrollbar_layer.cc
+++ b/cc/layers/painted_scrollbar_layer.cc
@@ -192,6 +192,9 @@ void PaintedScrollbarLayer::UpdateThumbAndTrackGeometry() {
   if (has_thumb_) {
     UpdateProperty(scrollbar_->ThumbThickness(), &thumb_thickness_);
     UpdateProperty(scrollbar_->ThumbLength(), &thumb_length_);
+  } else {
+    UpdateProperty(0, &thumb_thickness_);
+    UpdateProperty(0, &thumb_length_);
   }
 }