DevTools: Add JSDoc for static methods, fix JSDoc types and induced errors

Source/devtools/front_end/script_formatter_worker/ScriptFormatterWorker.js

Index: Source/devtools/front_end/script_formatter_worker/ScriptFormatterWorker.js
diff --git a/Source/devtools/front_end/script_formatter_worker/ScriptFormatterWorker.js b/Source/devtools/front_end/script_formatter_worker/ScriptFormatterWorker.js
index 5cc1bfed31e493c6bfaab113b88d5ef6d2987b84..d278ecb7eb5e7ba57e9f42c08174fffa19f21bb9 100644
--- a/Source/devtools/front_end/script_formatter_worker/ScriptFormatterWorker.js
+++ b/Source/devtools/front_end/script_formatter_worker/ScriptFormatterWorker.js
@@ -479,14 +479,6 @@ FormatterWorker.HTMLFormatter.prototype = {
     }
 }
 
-Array.prototype.keySet = function()
-{
-    var keys = {};
-    for (var i = 0; i < this.length; ++i)
-        keys[this[i]] = true;
-    return keys;
-};
-
 /**
  * @return {!Object}
  */