DevTools: Don't show blank placeholder in TextPrompt

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

 /*
  * Copyright (C) 2008 Apple Inc.  All rights reserved.
  * Copyright (C) 2011 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:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
@@ skipping 182 matching lines @@
   setTitle(title) {
     this._title = title;
     if (this._proxyElement)
       this._proxyElement.title = title;
   }
 
   /**
    * @param {string} placeholder
    */
   setPlaceholder(placeholder) {
-    this._element.setAttribute('data-placeholder', placeholder);
+    if (placeholder)
+      this._element.setAttribute('data-placeholder', placeholder);
+    else
+      this._element.removeAttribute('data-placeholder');
   }
 
   _removeFromElement() {
     this.clearAutocomplete();
     this._element.removeEventListener('keydown', this._boundOnKeyDown, false);
     this._element.removeEventListener('input', this._boundOnInput, false);
     this._element.removeEventListener('selectstart', this._boundClearAutocomplete, false);
     this._element.removeEventListener('blur', this._boundClearAutocomplete, false);
     this._element.ownerDocument.defaultView.removeEventListener('resize', this._boundClearAutocomplete, false);
     if (this._isEditing)
@@ skipping 421 matching lines @@
   }
 };
 
 UI.TextPrompt.DefaultAutocompletionTimeout = 250;
 
 /** @enum {symbol} */
 UI.TextPrompt.Events = {
   ItemApplied: Symbol('text-prompt-item-applied'),
   ItemAccepted: Symbol('text-prompt-item-accepted')
 };