Issue 354 - Avoid a string copy that is unnecessary most of the time

lib/filterClasses.js

Index: lib/filterClasses.js
===================================================================
--- a/lib/filterClasses.js
+++ b/lib/filterClasses.js
@@ -298,26 +298,38 @@ ActiveFilter.prototype =
   /**
    * Determines whether the trailing dot in domain names isn't important and
    * should be ignored, must be overridden by subclasses.
    * @type Boolean
    */
   ignoreTrailingDot: true,
 
   /**
+   * Determines whether domainSource is already upper-case,
+   * can be overridden by subclasses.
+   * @type Boolean
+   */
+  domainSourceIsUpperCase: false,
+
+  /**
    * Map containing domains that this filter should match on/not match on or null if the filter should match on all domains
    * @type Object
    */
   get domains()
   {
     let domains = null;
 
     if (this.domainSource)
     {
-      let list = this.domainSource.split(this.domainSeparator);
+      let source = this.domainSource;
+      if (!this.domainSourceIsUpperCase) {
+        // RegExpFilter already have uppercase domains
+        source = source.toUpperCase();
+      }
+      let list = source.split(this.domainSeparator);
       if (list.length == 1 && list[0][0] != "~")
       {
         // Fast track for the common one-domain scenario
         domains = {__proto__: null, "": false};
         if (this.ignoreTrailingDot)
           list[0] = list[0].replace(/\.+$/, "");
         domains[list[0]] = true;
       }
@@ -347,17 +359,17 @@ ActiveFilter.prototype =
           if (!domains)
             domains = {__proto__: null};
 
           domains[domain] = include;
         }
         domains[""] = !hasIncludes;
       }
 
-      delete this.domainSource;
+      this.domainSource = null;
     }
 
     this.__defineGetter__("domains", function() domains);
     return this.domains;
   },
 
   /**
    * Checks whether this filter is active on a domain.
@@ -462,16 +474,21 @@ function RegExpFilter(text, regexpSource
 }
 exports.RegExpFilter = RegExpFilter;
 
 RegExpFilter.prototype =
 {
   __proto__: ActiveFilter.prototype,
 
   /**
+   * @see ActiveFilter.domainSourceIsUpperCase
+   */
+  domainSourceIsUpperCase: true,
+
+  /**
    * Number of filters contained, will always be 1 (required to optimize Matcher).
    * @type Integer
    */
   length: 1,
 
   /**
    * @see ActiveFilter.domainSeparator
    */
@@ -740,17 +757,17 @@ WhitelistFilter.prototype =
  * @param {String} text see Filter()
  * @param {String} domains    (optional) Host names or domains the filter should be restricted to
  * @param {String} selector   CSS selector for the HTML elements that should be hidden
  * @constructor
  * @augments ActiveFilter
  */
 function ElemHideBase(text, domains, selector)
 {
-  ActiveFilter.call(this, text, domains ? domains.toUpperCase() : null);
+  ActiveFilter.call(this, text, domains || null);
 
   if (domains)
     this.selectorDomain = domains.replace(/,~[^,]+/g, "").replace(/^~[^,]+,?/, "").toLowerCase();
   this.selector = selector;
 }
 exports.ElemHideBase = ElemHideBase;
 
 ElemHideBase.prototype =