Use "\uFEFF" instead of "." in WebInspector.ViewportControl's gap elements.

third_party/WebKit/Source/devtools/front_end/ui/ViewportControl.js

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 19 matching lines @@
 
 /**
  * @constructor
  * @param {!WebInspector.ViewportControl.Provider} provider
  */
 WebInspector.ViewportControl = function(provider)
 {
     this.element = createElement("div");
     this.element.style.overflow = "auto";
     this._topGapElement = this.element.createChild("div");
-    this._topGapElement.textContent = ".";

[pfeldman, 2016/01/22 01:37:34]

lushnikov@ says that "." was here to render selection that spans beyond the
viewport prettier. and it seems it is no longer needed - either new selection
rendering helped or other things changed over time.

[skobes, 2016/01/22 01:51:53]

I first tried eliminating the text content but
inspector/console/console-viewport-selection.html failed.  I think the
range.intersectsNode calls in _updateSelectionModel depend on having non-empty
text content.

     this._topGapElement.style.height = "0px";

[pfeldman, 2016/01/22 01:37:34]

how come it contributes to the height? - it has zero height.

[skobes, 2016/01/22 01:51:53]

The text content produces overflow which contributes to the container's height. 
Example: https://jsbin.com/zisowo/edit?html,output

     this._topGapElement.style.color = "transparent";
     this._contentElement = this.element.createChild("div");
     this._bottomGapElement = this.element.createChild("div");
-    this._bottomGapElement.textContent = ".";
     this._bottomGapElement.style.height = "0px";
     this._bottomGapElement.style.color = "transparent";
 
+    // Text content needed for range intersection checks in _updateSelectionModel.
+    // Use Unicode ZERO WIDTH NO-BREAK SPACE, which avoids contributing any height to the element's layout overflow.
+    this._topGapElement.textContent = "\uFEFF";
+    this._bottomGapElement.textContent = "\uFEFF";
+
     this._provider = provider;
     this.element.addEventListener("scroll", this._onScroll.bind(this), false);
     this.element.addEventListener("copy", this._onCopy.bind(this), false);
     this.element.addEventListener("dragstart", this._onDragStart.bind(this), false);
 
     this._firstVisibleIndex = 0;
     this._lastVisibleIndex = -1;
     this._renderedItems = [];
     this._anchorSelection = null;
     this._headSelection = null;
@@ skipping 568 matching lines @@
 
     /**
      * @return {number}
      */
     _visibleHeight: function()
     {
         // Use offsetHeight instead of clientHeight to avoid being affected by horizontal scroll.
         return this.element.offsetHeight;
     }
 }