DevTools: [Styles] Add "px" suffix to numbers on arrow up/down

Source/devtools/front_end/elements/StylesSidebarPane.js

 /*
  * Copyright (C) 2007 Apple Inc.  All rights reserved.
  * Copyright (C) 2009 Joseph Pecoraro
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
@@ skipping 3267 matching lines @@
          * @param {string} originalValue
          * @param {string} replacementString
          * @this {WebInspector.StylesSidebarPane.CSSPropertyPrompt}
          */
         function finishHandler(originalValue, replacementString)
         {
             // Synthesize property text disregarding any comments, custom whitespace etc.
             this._sidebarPane.applyStyleText(this._sidebarPane.nameElement.textContent + ": " + this._sidebarPane.valueElement.textContent, false, false, false);
         }
 
+        /**
+         * @param {string} prefix
+         * @param {number} number
+         * @param {string} suffix
+         * @return {string}
+         * @this {WebInspector.StylesSidebarPane.CSSPropertyPrompt}
+         */
+        function customNumberHandler(prefix, number, suffix)
+        {
+            if (number !== 0 && !suffix.length && WebInspector.CSSMetadata.isLengthProperty(this._sidebarPane.property.name))
+                suffix = "px";
+            return prefix + number + suffix;
+        }
+
         // Handle numeric value increment/decrement only at this point.
-        if (!this._isEditingName && WebInspector.handleElementValueModifications(event, this._sidebarPane.valueElement, finishHandler.bind(this), this._isValueSuggestion.bind(this)))
+        if (!this._isEditingName && WebInspector.handleElementValueModifications(event, this._sidebarPane.valueElement, finishHandler.bind(this), this._isValueSuggestion.bind(this), customNumberHandler.bind(this)))
             return true;
 
         return false;
     },
 
     /**
      * @param {string} word
      * @return {boolean}
      */
     _isValueSuggestion: function(word)
@@ skipping 18 matching lines @@
             return;
         }
 
         var results = this._cssCompletions.startsWith(prefix);
         var selectedIndex = this._cssCompletions.mostUsedOf(results);
         completionsReadyCallback(results, selectedIndex);
     },
 
     __proto__: WebInspector.TextPrompt.prototype
 }