views: open context menus on extension actions on down arrow

These buttons have two modes: a context menu and an "activation", which usually
shows a popup but may also take an action on the page or similar. They
subclass MenuButton, so down-arrow is wired to activation instead of to opening
the menu by default. This change causes extension actions to always open their
context menu on down-arrow instead of activating, since otherwise the context
menu is keyboard-inaccessible.

Bug: 696268
Change-Id: If0f12c3ac5b1168cc74ea5df848ecf30d0662e09
Reviewed-on: https://chromium-review.googlesource.com/c/1286738Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Elly Fong-Jones <ellyjones@chromium.org>
Cr-Commit-Position: refs/heads/master@{#600736}

chrome/browser/ui/views/toolbar/toolbar_action_view.cc

@@ -144,6 +144,14 @@ ToolbarActionView::CreateInkDropHighlight() const {
   return CreateToolbarInkDropHighlight(this);
 }
 
+bool ToolbarActionView::OnKeyPressed(const ui::KeyEvent& event) {
+  if (event.key_code() == ui::VKEY_DOWN) {
+    ShowContextMenuForView(this, gfx::Point(), ui::MENU_SOURCE_KEYBOARD);
+    return true;
+  }
+  return MenuButton::OnKeyPressed(event);
+}
+
 content::WebContents* ToolbarActionView::GetCurrentWebContents() const {
   return delegate_->GetCurrentWebContents();
 }

chrome/browser/ui/views/toolbar/toolbar_action_view.h

@@ -73,6 +73,7 @@ class ToolbarActionView : public views::MenuButton,
   std::unique_ptr<views::InkDrop> CreateInkDrop() override;
   std::unique_ptr<views::InkDropHighlight> CreateInkDropHighlight()
       const override;
+  bool OnKeyPressed(const ui::KeyEvent& event) override;
 
   // ToolbarActionViewDelegateViews:
   content::WebContents* GetCurrentWebContents() const override;