DevTools: roll codemirror to @6d1379e29

The patch rolls CodeMirror to fix a wrong gutter background positioning.
This fixes the SourceCode-Diff experiment rendering in case of horizontal
source scroll.

BUG=none
R=einbinder

Review-Url: https://codereview.chromium.org/2201523002
Cr-Commit-Position: refs/heads/master@{#408826}

third_party/WebKit/Source/devtools/front_end/cm/codemirror.js

@@ -592,8 +592,12 @@
     var comp = compensateForHScroll(display) - display.scroller.scrollLeft + cm.doc.scrollLeft;
     var gutterW = display.gutters.offsetWidth, left = comp + "px";
     for (var i = 0; i < view.length; i++) if (!view[i].hidden) {
-      if (cm.options.fixedGutter && view[i].gutter)
+      if (cm.options.fixedGutter) {
+        if (view[i].gutter)
           view[i].gutter.style.left = left;
+        if (view[i].gutterBackground)
+          view[i].gutterBackground.style.left = left;
+      }
       var align = view[i].alignable;
       if (align) for (var j = 0; j < align.length; j++)
         align[j].style.left = left;