code: function _initialize($container) {
          if (_activePaneId) {
              throw new Error("MainViewManager has already been initialized");
          }
  
          _$el = $container;
          _createPaneIfNecessary(FIRST_PANE);
          _activePaneId = FIRST_PANE;
          // One-time init so the pane has the "active" appearance
          _panes[FIRST_PANE]._handleActivePaneChange(undefined, _activePaneId);
          _initialLayout();
  
          // This ensures that unit tests that use this function
          //  get an event handler for workspace events and we don't listen
          //  to the event before we've been initialized
          WorkspaceManager.on("workspaceUpdateLayout", _updateLayout);
  
          // Listen to key Alt-W to toggle between panes
          CommandManager.register(Strings.CMD_SWITCH_PANE_FOCUS, Commands.CMD_SWITCH_PANE_FOCUS, switchPaneFocus);
          KeyBindingManager.addBinding(Commands.CMD_SWITCH_PANE_FOCUS, {key: 'Alt-W'});
      }
docs: Initializes the MainViewManager's view state
  @param {jQuery} $container - the container where the main view will live
  @private