[DevTools] Check mappings.length in BlackboxManager on SourceMap loaded

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

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 /**
  * @constructor
  * @param {!WebInspector.DebuggerWorkspaceBinding} debuggerWorkspaceBinding
  * @param {!WebInspector.NetworkMapping} networkMapping
  */
 WebInspector.BlackboxManager = function(debuggerWorkspaceBinding, networkMapping)
@@ skipping 99 matching lines @@
         var previousScriptState = this._scriptPositions(script);
         if (!previousScriptState)
             return Promise.resolve();
 
         var mappings = sourceMap.mappings().slice();
         mappings.sort(mappingComparator);
 
         if (!mappings.length) {
             if (previousScriptState.length > 0)
                 return this._setScriptState(script, []);
+            return Promise.resolve();
         }
 
         var currentBlackboxed = false;
         var isBlackboxed = false;
         var positions = [];
         // If content in script file begin is not mapped and one or more ranges are blackboxed then blackbox it.
         if (mappings[0].lineNumber !== 0 || mappings[0].columnNumber !== 0) {
             positions.push({ line: 0, column: 0});
             currentBlackboxed = true;
         }
@@ skipping 281 matching lines @@
             if (scheme === "chrome-extension")
                 prefix += parsedURL.host + "\\b";
             prefix += ".*";
         }
         return prefix + name.escapeForRegExp() + (url.endsWith(name) ? "$" : "\\b");
     }
 }
 
 /** @type {!WebInspector.BlackboxManager} */
 WebInspector.blackboxManager;