WebUI Tab Strip: Set keyboard focus when opening via keyboard

If the tab strip was opened using a keyboard (and not touch), the view
now tells the UI handler to inform the front-end that keyboard focus
has moved into the tab strip. The front-end will automatically focus the
first tab and add the focus indicators.

Bug: 1135358
Change-Id: I3524e186638c61c128af9d1041d5573774ba14bf
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2449941Reviewed-by: Collin Baker <collinbaker@chromium.org>
Commit-Queue: John Lee <johntlee@chromium.org>
Cr-Commit-Position: refs/heads/master@{#814022}

chrome/browser/ui/views/frame/webui_tab_strip_container_view.cc

@@ -659,7 +659,7 @@ void WebUITabStripContainerView::EndDragToOpen(
                    : WebUITabStripOpenCloseReason::kDragRelease);
 }
 
-void WebUITabStripContainerView::TabCounterPressed() {
+void WebUITabStripContainerView::TabCounterPressed(const ui::Event& event) {
   const bool new_visibility = !GetVisible();
   if (new_visibility) {
     RecordTabStripUIOpenHistogram(TabStripUIOpenAction::kTapOnTabCounter);
@@ -676,9 +676,9 @@ void WebUITabStripContainerView::TabCounterPressed() {
   SetContainerTargetVisibility(new_visibility,
                                WebUITabStripOpenCloseReason::kOther);
 
-  if (GetVisible() && tab_counter_->HasFocus()) {
-    // Automatically move focus to the tab strip WebUI if the focus is
-    // currently on the toggle button.
+  if (GetVisible() && event.IsKeyEvent()) {
+    // Automatically move focus to the tab strip WebUI if the tab strip
+    // was opened via a key event.
     SetPaneFocusAndFocusDefault();
   }
 }

chrome/browser/ui/views/frame/webui_tab_strip_container_view.h

@@ -96,7 +96,7 @@ class WebUITabStripContainerView : public TabStripUIEmbedder,
   void EndDragToOpen(base::Optional<WebUITabStripDragDirection>
                          fling_direction = base::nullopt);
 
-  void TabCounterPressed();
+  void TabCounterPressed(const ui::Event& event);
 
   void SetContainerTargetVisibility(bool target_visible,
                                     WebUITabStripOpenCloseReason reason);