[Devtools] Lazily build reverse mappings

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
  * @implements {WebInspector.TargetManager.Observer}
  */
 WebInspector.BlackboxManager = function(debuggerWorkspaceBinding)
@@ skipping 131 matching lines @@
      * @return {!Promise<undefined>}
      */
     sourceMapLoaded: function(script, sourceMap)
     {
         if (!sourceMap)
             return Promise.resolve();
         var previousScriptState = this._scriptPositions(script);
         if (!previousScriptState)
             return Promise.resolve();
 
-        var mappings = sourceMap.mappings().slice();
-        mappings.sort(mappingComparator);
-
+        var hasBlackboxedMappings = sourceMap.sourceURLs().some((url) => this.isBlackboxedURL(url));
+        var mappings = hasBlackboxedMappings ? sourceMap.mappings().slice() : [];
         if (!mappings.length) {

[lushnikov, 2016/10/01 04:23:50]

how's a sourceMap with empty mappings differs from a "no sourcemap" case?

@kozyatinskiy: could you please give some insights on this?

[kozy, 2016/10/01 04:40:21]

There are no big difference between empty source map and no source map. This
cases can be merge into no mappings case.

lgtm for blackboxmanager.

             if (previousScriptState.length > 0)
                 return this._setScriptState(script, []);
             return Promise.resolve();
         }
+        mappings.sort(mappingComparator);
 
         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({ lineNumber: 0, columnNumber: 0});
             currentBlackboxed = true;
         }
         for (var mapping of mappings) {
@@ skipping 276 matching lines @@
             if (scheme === "chrome-extension")
                 prefix += parsedURL.host + "\\b";
             prefix += ".*";
         }
         return prefix + name.escapeForRegExp() + (url.endsWith(name) ? "$" : "\\b");
     }
 }
 
 /** @type {!WebInspector.BlackboxManager} */
 WebInspector.blackboxManager;