[TabGroupModelFilter] Fix crash on undo last closed tab

The cause is TabModel#setIndex() event is fired when undoing the first
tab, before the tab actually undo in TabGroupModelFilter.

This CL is a band-aid fix for M74. We cache the selected tab that is not
exist in the TabGroupFilterModel. And try to select that tab on the
next addTab()/undo call. This will fix the current crash and will not
causing any side effects on TabGroupModelFilter normal usage.

Bug: 948518
Change-Id: Ic65e521baebe65c54b1033f6be35dd2dbdd1a676
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1552281Reviewed-by: Wei-Yin Chen (陳威尹) <wychen@chromium.org>
Reviewed-by: Yusuf Ozuysal <yusufo@chromium.org>
Commit-Queue: Mei Liang <meiliang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#648363}

chrome/android/java/src/org/chromium/chrome/browser/tabmodel/TabModelFilter.java

@@ -110,10 +110,20 @@ public abstract class TabModelFilter extends EmptyTabModelObserver implements Ta
      */
     protected abstract void reorder();
 
+    // TODO(crbug.com/948518): This is a band-aid fix for not crashing when undo the last closed
+    // tab, should remove later.
+    /**
+     * @return Whether filter should notify observers about the SetIndex call.
+     */
+    protected boolean shouldNotifyObserversOnSetIndex() {
+        return true;
+    }
+
     // TabModelObserver implementation.
     @Override
     public void didSelectTab(Tab tab, int type, int lastId) {
         selectTab(tab);
+        if (!shouldNotifyObserversOnSetIndex()) return;
         for (TabModelObserver observer : mFilteredObservers) {
             observer.didSelectTab(tab, type, lastId);
         }

chrome/android/java/src/org/chromium/chrome/browser/tasks/tabgroup/TabGroupModelFilter.java

@@ -103,6 +103,7 @@ public class TabGroupModelFilter extends TabModelFilter {
     private int mCurrentGroupIndex = TabList.INVALID_TAB_INDEX;
     // The number of groups with at least 2 tabs.
     private int mActualGroupCount;
+    private Tab mAbsentSelectedTab;
 
     public TabGroupModelFilter(TabModel tabModel) {
         super(tabModel);
@@ -165,6 +166,12 @@ public class TabGroupModelFilter extends TabModelFilter {
             mGroupIdToGroupMap.put(groupId, tabGroup);
             mGroupIdToGroupIndexMap.put(groupId, mGroupIdToGroupIndexMap.size());
         }
+
+        if (mAbsentSelectedTab != null) {
+            Tab absentSelectedTab = mAbsentSelectedTab;
+            mAbsentSelectedTab = null;
+            selectTab(absentSelectedTab);
+        }
     }
 
     @Override
@@ -198,9 +205,14 @@ public class TabGroupModelFilter extends TabModelFilter {
 
     @Override
     protected void selectTab(Tab tab) {
+        assert mAbsentSelectedTab == null;
         int groupId = tab.getRootId();
-        mGroupIdToGroupMap.get(groupId).setLastShownTabId(tab.getId());
-        mCurrentGroupIndex = mGroupIdToGroupIndexMap.get(groupId);
+        if (mGroupIdToGroupMap.get(groupId) == null) {
+            mAbsentSelectedTab = tab;
+        } else {
+            mGroupIdToGroupMap.get(groupId).setLastShownTabId(tab.getId());
+            mCurrentGroupIndex = mGroupIdToGroupIndexMap.get(groupId);
+        }
     }
 
     @Override
@@ -232,6 +244,11 @@ public class TabGroupModelFilter extends TabModelFilter {
         }
     }
 
+    @Override
+    protected boolean shouldNotifyObserversOnSetIndex() {
+        return mAbsentSelectedTab == null;
+    }
+
     // TabList implementation.
     @Override
     public boolean isIncognito() {