Explicitly set gutter height

This prevents it from being repainted whenever the height of the inner
editor briefly changes during a repaint. (At least, it does on Webkit).

Issue #1514

lib/codemirror.css

@@ -149,7 +149,6 @@ div.CodeMirror span.CodeMirror-nonmatchingbracket {color: #f22;}
 
 .CodeMirror-gutters {
   position: absolute; left: 0; top: 0;
-  height: 100%;
   padding-bottom: 30px;
   z-index: 3;
 }

lib/codemirror.js

@@ -127,10 +127,8 @@ window.CodeMirror = (function() {
     // Will contain the gutters, if any
     d.gutters = elt("div", null, "CodeMirror-gutters");
     d.lineGutter = null;
-    // Helper element to properly size the gutter backgrounds
-    var scrollerInner = elt("div", [d.sizer, d.heightForcer, d.gutters], null, "position: relative; min-height: 100%");
     // Provides scrolling
-    d.scroller = elt("div", [scrollerInner], "CodeMirror-scroll");
+    d.scroller = elt("div", [d.sizer, d.heightForcer, d.gutters], "CodeMirror-scroll");
     d.scroller.setAttribute("tabIndex", "-1");
     // The element in which the editor lives.
     d.wrapper = elt("div", [d.inputDiv, d.scrollbarH, d.scrollbarV,
@@ -323,6 +321,7 @@ window.CodeMirror = (function() {
     var d = cm.display, docHeight = cm.doc.height;
     var totalHeight = docHeight + paddingVert(d);
     d.sizer.style.minHeight = d.heightForcer.style.top = totalHeight + "px";
+    d.gutters.style.height = Math.max(totalHeight, d.scroller.clientHeight - scrollerCutOff) + "px";
     var scrollHeight = Math.max(totalHeight, d.scroller.scrollHeight);
     var needsH = d.scroller.scrollWidth > d.scroller.clientWidth;
     var needsV = scrollHeight > d.scroller.clientHeight;