code: function(propertyText, majorChange, overwrite, userCallback)
      {
          function enabledCallback(style)
          {
              if (userCallback)
                  userCallback(style);
          }
  
          function callback(error, stylePayload)
          {
              WebInspector.cssModel._pendingCommandsMajorState.pop();
              if (!error) {
                  if (majorChange)
                      WebInspector.domAgent.markUndoableState();
                  this.text = propertyText;
                  var style = WebInspector.CSSStyleDeclaration.parsePayload(stylePayload);
                  var newProperty = style.allProperties[this.index];
  
                  if (newProperty && this.disabled && !propertyText.match(/^\s*$/)) {
                      newProperty.setDisabled(false, enabledCallback);
                      return;
                  }
  
                  if (userCallback)
                      userCallback(style);
              } else {
                  if (userCallback)
                      userCallback(null);
              }
          }
  
          if (!this.ownerStyle)
              throw "No ownerStyle for property";
  
          // An index past all the properties adds a new property to the style.
          WebInspector.cssModel._pendingCommandsMajorState.push(majorChange);
          CSSAgent.setPropertyText(this.ownerStyle.id, this.index, propertyText, overwrite, callback.bind(this));
      }
docs: Replaces "propertyName: propertyValue [!important];" in the stylesheet by an arbitrary propertyText.
  
  @param {string} propertyText
  @param {boolean} majorChange
  @param {boolean} overwrite
  @param {Function=} userCallback