DevTools: TabbedLocations only materialize tabs when needed

TabbedLocations used to materialize tab contents on tabSelected. Now,
they materialize only if the tab is selected while the TabbedPane is showing, or
when the TabbedPane is being shown.

BUG=none

Review-Url: https://codereview.chromium.org/2617293002
Cr-Commit-Position: refs/heads/master@{#442824}

third_party/WebKit/Source/devtools/front_end/ui/View.js

@@ -442,6 +442,13 @@ UI.ViewManager._ContainerWidget = class extends UI.VBox {
     this._materializePromise = Promise.all(promises);
     return this._materializePromise;
   }
+
+  /**
+   * @override
+   */
+  wasShown() {
+    this._materialize();
+  }
 };
 
 /**
@@ -709,7 +716,8 @@ UI.ViewManager._TabbedLocation = class extends UI.ViewManager._Location {
     this.appendView(view, insertBefore);
     this._tabbedPane.selectTab(view.viewId());
     this._tabbedPane.focus();
-    return this._materializeWidget(view);
+    var widget = /** @type {!UI.ViewManager._ContainerWidget} */ (this._tabbedPane.tabView(view.viewId()));
+    return widget._materialize();
   }
 
   /**
@@ -737,8 +745,6 @@ UI.ViewManager._TabbedLocation = class extends UI.ViewManager._Location {
     if (!view)
       return;
 
-    this._materializeWidget(view);
-
     if (view.isCloseable()) {
       var tabs = this._closeableTabSetting.get();
       if (!tabs[tabId]) {
@@ -760,15 +766,6 @@ UI.ViewManager._TabbedLocation = class extends UI.ViewManager._Location {
     }
   }
 
-  /**
-   * @param {!UI.View} view
-   * @return {!Promise}
-   */
-  _materializeWidget(view) {
-    var widget = /** @type {!UI.ViewManager._ContainerWidget} */ (this._tabbedPane.tabView(view.viewId()));
-    return widget._materialize();
-  }
-
   /**
    * @param {!Common.Event} event
    */