Fix crashing in TabGroup

The assertions wouldn't hold for frozen and external tabs. Convert
to early return.

Bug: 947902
Change-Id: Ia1411a59fea2165f78bca5fabc2d3d35d8825bda
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1548033
Commit-Queue: Wei-Yin Chen (陳威尹) <wychen@chromium.org>
Reviewed-by: Yusuf Ozuysal <yusufo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#646464}

chrome/android/features/tab_ui/java/src/org/chromium/chrome/browser/tasks/tab_management/TabListMediator.java

@@ -257,23 +257,19 @@ class TabListMediator {
 
     private void onTabAdded(Tab tab, boolean onlyShowRelatedTabs) {
         List<Tab> related = getRelatedTabsForId(tab.getId());
+        int index;
         if (onlyShowRelatedTabs) {
-            int index = related.indexOf(tab);
-            assert index != -1;
-            addTabInfoToModel(tab, index, mTabModelSelector.getCurrentTab() == tab);
+            index = related.indexOf(tab);
+            if (index == -1) return;
         } else {
-            int index = TabModelUtils.getTabIndexById(
+            index = TabModelUtils.getTabIndexById(
                     mTabModelSelector.getTabModelFilterProvider().getCurrentTabModelFilter(),
                     tab.getId());
-            if (related.size() > 1) {
-                // Skip all but one tab in a tab group.
-                if (index == TabList.INVALID_TAB_INDEX) return;
-                // TODO(wychen): the title (tab count in the group) is wrong when it's not the last
-                //  tab added in the group.
-            }
-            assert index != TabList.INVALID_TAB_INDEX;
-            addTabInfoToModel(tab, index, mTabModelSelector.getCurrentTab() == tab);
+            // TODO(wychen): the title (tab count in the group) is wrong when it's not the last
+            //  tab added in the group.
+            if (index == TabList.INVALID_TAB_INDEX) return;
         }
+        addTabInfoToModel(tab, index, mTabModelSelector.getCurrentTab() == tab);
     }
 
     /**