Turn off the pseudo-scrollbar on OS X Lion

This is a temporary kludge. I hope we'll be able to find a better
solution. (This should bring back the flicker issue on Lion.)

Issue #727

lib/codemirror.js

@@ -52,16 +52,13 @@ var CodeMirror = (function() {
     // Needed to handle Tab key in KHTML
     if (khtml) inputDiv.style.height = "1px", inputDiv.style.position = "absolute";
 
-    // Check for OS X >= 10.7. If so, we need to force a width on the scrollbar, and
-    // make it overlap the content. (But we only do this if the scrollbar doesn't already
-    // have a natural width. If the mouse is plugged in or the user sets the system pref
-    // to always show scrollbars, the scrollbar shouldn't overlap.)
-    if (mac_geLion) {
-      scrollbar.className += (overlapScrollbars() ? " cm-sb-overlap" : " cm-sb-nonoverlap");
-    } else if (ie_lt8) {
-      // Need to set a minimum width to see the scrollbar on IE7 (but must not set it on IE8).
-      scrollbar.className += " cm-sb-ie7";
-    }
+    // Check for OS X >= 10.7. This has transparent scrollbars, so the
+    // overlaying of one scrollbar with another won't work. This is a
+    // temporary hack to simply turn off the overlay scrollbar. See
+    // issue #727.
+    if (mac_geLion) scrollbar.style.display = "none";
+    // Need to set a minimum width to see the scrollbar on IE7 (but must not set it on IE8).
+    else if (ie_lt8) scrollbar.style.minWidth = "18px";
 
     // Check for problem with IE innerHTML not working when we have a
     // P (or similar) parent node.
@@ -867,18 +864,6 @@ var CodeMirror = (function() {
       mover.style.top = displayOffset * textHeight() + "px";
     }
 
-    // On Mac OS X Lion and up, detect whether the mouse is plugged in by measuring
-    // the width of a div with a scrollbar in it. If the width is <= 1, then
-    // the mouse isn't plugged in and scrollbars should overlap the content.
-    function overlapScrollbars() {
-      var tmpSbInner = elt("div", null, "CodeMirror-scrollbar-inner", "height: 200px");
-      var tmpSb = elt("div", [tmpSbInner], "CodeMirror-scrollbar", "position: absolute; left: -9999px; height: 100px;");
-      document.body.appendChild(tmpSb);
-      var result = (tmpSb.offsetWidth <= 1);
-      document.body.removeChild(tmpSb);
-      return result;
-    }
-
     function computeMaxLength() {
       maxLine = getLine(0); maxLineChanged = true;
       var maxLineLength = maxLine.text.length;