Allow TabStripModel::GetTabGroupForTab to be called for any index.

Index can be out of bounds when attaching to a new tabstrip.

Bug: 915956
Change-Id: Id921c4232f7e081b7d821f6722ff2ba7994ade76
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1670125
Commit-Queue: Charlene Yan <cyan@chromium.org>
Reviewed-by: Bret Sepulveda <bsep@chromium.org>
Cr-Commit-Position: refs/heads/master@{#671507}

chrome/browser/ui/tabs/tab_strip_model.cc

@@ -781,7 +781,7 @@ const TabGroupData* TabStripModel::GetDataForGroup(TabGroupId group) const {
 }
 
 base::Optional<TabGroupId> TabStripModel::GetTabGroupForTab(int index) const {
-  return (index == kNoTab) ? base::nullopt : contents_data_[index]->group();
+  return ContainsIndex(index) ? contents_data_[index]->group() : base::nullopt;
 }
 
 std::vector<TabGroupId> TabStripModel::ListTabGroups() const {

chrome/browser/ui/tabs/tab_strip_model.h

@@ -319,9 +319,10 @@ class TabStripModel {
   // Returns true if the tab at |index| is blocked by a tab modal dialog.
   bool IsTabBlocked(int index) const;
 
-  // Returns the group that contains the tab at |index|, or nullopt if it is not
-  // grouped. This feature is in development and gated behind a feature flag
-  // (see https://crbug.com/915956).
+  // Returns the group that contains the tab at |index|, or nullopt if the tab
+  // index is invalid or not grouped.
+  // This feature is in development and gated behind a feature flag (see
+  // https://crbug.com/915956).
   base::Optional<TabGroupId> GetTabGroupForTab(int index) const;
 
   // Returns the TabGroupData instance for the given |group|.