Stop spurious feedback panels being displayed

Panel items can be created and attached to a a display panel by
calling createPanelItem() followed by attachPanelItem() and they
can be removed by calling removePanelItem().

Change the API surface for attaching panel items to ignore panel
items that have already been removed using removePanelItem().

Bug: 1006124
Tests: Updated browser_tests --gtest_filter="FileManagerJsTest.FilesDisplayPanel"
Change-Id: Id7dce8496f4a5cf2090b9071404bd45b5033ae07
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1819078Reviewed-by: Noel Gordon <noel@chromium.org>
Commit-Queue: Alex Danilo <adanilo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#698833}

ui/file_manager/file_manager/foreground/elements/files_xf_elements_unittest.js

@@ -61,12 +61,35 @@ async function testFilesDisplayPanel(done) {
   assertTrue(displayPanel.findPanelItemById('testpanel1') === null);
 
   // Add another panel item and confirm the expanded state persists by
-  // checking the pnel container is not hidden and there is a summary panel.
+  // checking the panel container is not hidden and there is a summary panel.
   progressPanel = displayPanel.addPanelItem('testpanel1');
   progressPanel.panelType = progressPanel.panelTypeProgress;
   assertFalse(panelContainer.hasAttribute('hidden'));
   summaryPanelItem = summaryContainer.querySelector('xf-panel-item');
   assertTrue(summaryPanelItem.panelType === summaryPanelItem.panelTypeSummary);
 
+  // Test create/attach/remove sequences.
+  // Create a progress panel item.
+  progressPanel = displayPanel.createPanelItem('testpanel2');
+  progressPanel.panelType = progressPanel.panelTypeProgress;
+  // Attach the panel to it's host display panel.
+  displayPanel.attachPanelItem(progressPanel);
+  // Verify the panel is attached to the document.
+  assertTrue(!!progressPanel.parentNode);
+  // Remove the panel item.
+  displayPanel.removePanelItem(progressPanel);
+  // Verify the panel item is not attached to the document.
+  assertTrue(progressPanel.parentNode === null);
+
+  // Create a progress panel item.
+  progressPanel = displayPanel.createPanelItem('testpanel3');
+  progressPanel.panelType = progressPanel.panelTypeProgress;
+  // Remove the panel item.
+  displayPanel.removePanelItem(progressPanel);
+  // Try to attach the removed panel to it's host display panel.
+  displayPanel.attachPanelItem(progressPanel);
+  // Verify the panel is not attached to the document.
+  assertTrue(progressPanel.parentNode === null);
+
   done();
 }

ui/file_manager/file_manager/foreground/elements/xf_display_panel.js

@@ -327,6 +327,11 @@ class DisplayPanel extends HTMLElement {
    */
   attachPanelItem(panel) {
     const displayPanel = panel.parent;
+    // Only attach the panel if it hasn't been removed.
+    const index = displayPanel.items_.indexOf(panel);
+    if (index === -1) {
+      return;
+    }
     displayPanel.panels_.appendChild(panel);
     displayPanel.updateSummaryPanel();
   }