(defvar gc 0)
(defvar he 0)
(add-hook 'post-gc-hook (lambda () (setq gc (1+ gc))))
(defun show-gc-he () (message "gc: %s ... he: %s" gc he))
(add-hook 'post-command-hook 'show-gc-he)

(defun mode-line-default-help-echo (window)
  "Return default help echo text for WINDOW's mode line."
  (let* ((frame (window-frame window))
         (line-1a
          ;; Show text to select window only if the window is not
          ;; selected.
          (not (eq window (frame-selected-window frame))))
         (line-1b
          ;; Show text to drag mode line if either the window is not
          ;; at the bottom of its frame or the minibuffer window of
          ;; this frame can be resized.  This matches a corresponding
          ;; check in `mouse-drag-mode-line'.
          (or (not (window-at-side-p window 'bottom))
              (let ((mini-window (minibuffer-window frame)))
                (and (eq frame (window-frame mini-window))
                     (or (minibuffer-window-active-p mini-window)
                         (not resize-mini-windows))))))
         (line-2
          ;; Show text make window occupy the whole frame
          ;; only if it doesn't already do that.
          (not (eq window (frame-root-window frame))))
         (line-3
          ;; Show text to delete window only if that's possible.
          (not (eq window (frame-root-window frame)))))
    (setq he (1+ he))
    (when (or line-1a line-1b line-2 line-3)
      (concat
       (when (or line-1a line-1b)
         (concat
          "mouse-1: "
          (when line-1a "Select window")
          (when line-1b
            (if line-1a " (drag to resize)" "Drag to resize"))
          (when (or line-2 line-3) "\n")))
       (when line-2
         (concat
          "mouse-2: Make window occupy whole frame"
          (when line-3 "\n")))
       (when line-3
         "mouse-3: Remove window from frame")))))