DevTools: do not assign empty content to CSS UISourceCode in case of protocol error

third_party/WebKit/Source/devtools/front_end/bindings/StylesSourceMapping.js

 /*
  * Copyright (C) 2012 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 251 matching lines @@
       return;
     header.requestContent().then(callback.bind(this, uiSourceCode));
 
     /**
      * @param {!Workspace.UISourceCode} uiSourceCode
      * @param {?string} content
      * @this {Bindings.StylesSourceMapping}
      */
     function callback(uiSourceCode, content) {
       var styleFile = this._styleFiles.get(uiSourceCode);
-      if (styleFile)
-        styleFile.addRevision(content || '');
+      if (typeof content === 'string' && styleFile)
+        styleFile.addRevision(content);
+      this._styleFileSyncedForTest();
     }
   }
 
+  _styleFileSyncedForTest() {
+  }
+
   dispose() {
     Common.EventTarget.removeEventListeners(this._eventListeners);
   }
 };
 
 Bindings.StylesSourceMapping.ChangeUpdateTimeoutMs = 200;
 
 /**
  * @unrestricted
  */
@@ skipping 65 matching lines @@
 
   dispose() {
     if (this._terminated)
       return;
     this._terminated = true;
     Common.EventTarget.removeEventListeners(this._eventListeners);
   }
 };
 
 Bindings.StyleFile.updateTimeout = 200;