DevTools: Add a checkbox to enable async stacks in the sidebar header.

Source/devtools/front_end/DebuggerModel.js

 /*
  * Copyright (C) 2010 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 32 matching lines @@
     /** @type {!Object.<!string, !Array.<!WebInspector.Script>>} */
     this._scriptsBySourceURL = {};
 
     this._canSetScriptSource = false;
     this._breakpointsActive = true;
 
     WebInspector.settings.pauseOnExceptionStateString = WebInspector.settings.createSetting("pauseOnExceptionStateString", WebInspector.DebuggerModel.PauseOnExceptionsState.DontPauseOnExceptions);
     WebInspector.settings.pauseOnExceptionStateString.addChangeListener(this._pauseOnExceptionStateChanged, this);
 
     WebInspector.settings.enableAsyncStackTraces.addChangeListener(this._asyncStackTracesStateChanged, this);
-    WebInspector.settings.maxAsyncStackTraceDepth.addChangeListener(this._asyncStackTracesStateChanged, this);
 
     this.enableDebugger();
 
     WebInspector.DebuggerModel.applySkipStackFrameSettings();
 }
 
 // Keep these in sync with WebCore::ScriptDebugServer
 WebInspector.DebuggerModel.PauseOnExceptionsState = {
     DontPauseOnExceptions : "none",
     PauseOnAllExceptions : "all",
@@ skipping 109 matching lines @@
         this.dispatchEventToListeners(WebInspector.DebuggerModel.Events.DebuggerWasEnabled);
     },
 
     _pauseOnExceptionStateChanged: function()
     {
         DebuggerAgent.setPauseOnExceptions(WebInspector.settings.pauseOnExceptionStateString.get());
     },
 
     _asyncStackTracesStateChanged: function()
     {
+        const maxAsyncStackChainDepth = 4;
         var enabled = WebInspector.settings.enableAsyncStackTraces.get();
-        var depth = enabled ? Number(WebInspector.settings.maxAsyncStackTraceDepth.get()) : 0;
-        DebuggerAgent.setAsyncCallStackDepth(depth);
+        DebuggerAgent.setAsyncCallStackDepth(enabled ? maxAsyncStackChainDepth : 0);
     },
 
     _debuggerWasDisabled: function()
     {
         this._debuggerEnabled = false;
         this.dispatchEventToListeners(WebInspector.DebuggerModel.Events.DebuggerWasDisabled);
     },
 
     /**
      * @param {!WebInspector.DebuggerModel.Location} rawLocation
@@ skipping 859 matching lines @@
             this.callFrames[i].dispose();
         if (this.asyncStackTrace)
             this.asyncStackTrace.dispose();
     }
 }
 
 /**
  * @type {?WebInspector.DebuggerModel}
  */
 WebInspector.debuggerModel = null;