[Tab Groups] Check tab group of opener when adding a new tab.

When adding a new tab, look at the current active tab to
determine the group the new tab should belong in.

Bug: 1061004
Change-Id: I45905ccb9d57c5293059c9dc10ae7ad539c9fcb0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2107421
Commit-Queue: Charlene Yan <cyan@chromium.org>
Reviewed-by: Connie Wan <connily@chromium.org>
Cr-Commit-Position: refs/heads/master@{#751216}

chrome/browser/ui/tabs/tab_strip_model.cc

@@ -935,6 +935,11 @@ void TabStripModel::AddWebContents(
     index = order_controller_->DetermineInsertionIndex(transition,
                                                        add_types & ADD_ACTIVE);
     inherit_opener = true;
+
+    // The current active index is our opener. If the tab we are adding is not
+    // in a group, set the group of the tab to that of its opener.
+    if (!group.has_value())
+      group = GetTabGroupForTab(active_index());
   } else {
     // For all other types, respect what was passed to us, normalizing -1s and
     // values that are too large.

chrome/browser/ui/tabs/tab_strip_model_unittest.cc

@@ -1712,6 +1712,33 @@ TEST_F(TabStripModelTest, AddWebContents_ForgetOpeners) {
   EXPECT_TRUE(tabstrip.empty());
 }
 
+// Tests whether or not a WebContents in a new tab belongs in the same tab
+// group as its opener.
+TEST_F(TabStripModelTest, AddWebContents_LinkOpensInSameGroupAsOpener) {
+  TestTabStripModelDelegate delegate;
+  TabStripModel tabstrip(&delegate, profile());
+  ASSERT_TRUE(tabstrip.empty());
+
+  // Open the home page and add the tab to a group.
+  std::unique_ptr<WebContents> homepage_contents = CreateWebContents();
+  tabstrip.AddWebContents(std::move(homepage_contents), -1,
+                          ui::PAGE_TRANSITION_AUTO_BOOKMARK,
+                          TabStripModel::ADD_ACTIVE);
+  ASSERT_EQ(1, tabstrip.count());
+  tab_groups::TabGroupId group_id = tabstrip.AddToNewGroup({0});
+  ASSERT_EQ(tabstrip.GetTabGroupForTab(0), group_id);
+
+  // Open a tab by simulating a link that opens in a new tab.
+  std::unique_ptr<WebContents> contents = CreateWebContents();
+  tabstrip.AddWebContents(std::move(contents), -1, ui::PAGE_TRANSITION_LINK,
+                          TabStripModel::ADD_ACTIVE);
+  EXPECT_EQ(2, tabstrip.count());
+  EXPECT_EQ(tabstrip.GetTabGroupForTab(1), group_id);
+
+  tabstrip.CloseAllTabs();
+  ASSERT_TRUE(tabstrip.empty());
+}
+
 // Added for http://b/issue?id=958960
 TEST_F(TabStripModelTest, AppendContentsReselectionTest) {
   TestTabStripModelDelegate delegate;