DevTools: promisify ContentProvider.requestContent and all its clients.

third_party/WebKit/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 451 matching lines @@
         }
     },
 
     /**
      * @param {?WebInspector.CSSStyleSheetHeader} styleSheetHeader
      */
     _createNewRuleInStyleSheet: function(styleSheetHeader)
     {
         if (!styleSheetHeader)
             return;
-        styleSheetHeader.requestContent(onStyleSheetContent.bind(this, styleSheetHeader.id));
+        styleSheetHeader.requestContent().then(onStyleSheetContent.bind(this, styleSheetHeader.id));
 
         /**
          * @param {string} styleSheetId
-         * @param {string} text
+         * @param {?string} text
          * @this {WebInspector.StylesSidebarPane}
          */
         function onStyleSheetContent(styleSheetId, text)
         {
+            text = text || "";
             var lines = text.split("\n");
             var range = WebInspector.TextRange.createFromLocation(lines.length - 1, lines[lines.length - 1].length);
             this._addBlankSection(this._sectionBlocks[0].sections[0], styleSheetId, range);
         }
     },
 
     /**
      * @param {!WebInspector.StylePropertiesSection} insertAfterSection
      * @param {string} styleSheetId
      * @param {!WebInspector.TextRange} ruleLocation
@@ skipping 2474 matching lines @@
     WebInspector.context.addFlavorChangeListener(WebInspector.DOMNode, onNodeChanged);
     onNodeChanged();
     return button;
 
     function onNodeChanged()
     {
         var node = WebInspector.context.flavor(WebInspector.DOMNode);
         button.setEnabled(!!node);
     }
 }