assistant: handle back button

When caption bar shows back button, it should be equivalent to clicking
the back button.

Bug: b:113048612
Test: locally build and test
Change-Id: I7b388d784e24d43ffcf863103d7746998e573a4a
Reviewed-on: https://chromium-review.googlesource.com/1205673Reviewed-by: Muyuan Li <muyuanli@chromium.org>
Commit-Queue: Xiaohui Chen <xiaohuic@chromium.org>
Cr-Commit-Position: refs/heads/master@{#588933}

ash/assistant/ui/caption_bar.cc

@@ -47,6 +47,20 @@ CaptionBar::CaptionBar() {
 
 CaptionBar::~CaptionBar() = default;
 
+bool CaptionBar::AcceleratorPressed(const ui::Accelerator& accelerator) {
+  switch (accelerator.key_code()) {
+    case ui::VKEY_BROWSER_BACK:
+      HandleButton(CaptionButtonId::kBack);
+      break;
+    default:
+      NOTREACHED();
+      return false;
+  }
+
+  // Don't let DialogClientView handle the accelerator.
+  return true;
+}
+
 gfx::Size CaptionBar::CalculatePreferredSize() const {
   return gfx::Size(INT_MAX, GetHeightForWidth(INT_MAX));
 }
@@ -55,6 +69,17 @@ int CaptionBar::GetHeightForWidth(int width) const {
   return kPreferredHeightDip;
 }
 
+void CaptionBar::ButtonPressed(views::Button* sender, const ui::Event& event) {
+  auto id = static_cast<CaptionButtonId>(sender->id());
+  HandleButton(id);
+}
+
+void CaptionBar::SetButtonVisible(CaptionButtonId id, bool visible) {
+  views::View* button = GetViewByID(static_cast<int>(id));
+  if (button)
+    button->SetVisible(visible);
+}
+
 void CaptionBar::InitLayout() {
   views::BoxLayout* layout_manager =
       SetLayoutManager(std::make_unique<views::BoxLayout>(
@@ -87,10 +112,13 @@ void CaptionBar::InitLayout() {
       CreateCaptionButton(kWindowControlCloseIcon, IDS_APP_ACCNAME_CLOSE, this);
   close_button->set_id(static_cast<int>(CaptionButtonId::kClose));
   AddChildView(close_button);
+
+  AddAccelerator(ui::Accelerator(ui::VKEY_BROWSER_BACK, ui::EF_NONE));
 }
 
-void CaptionBar::ButtonPressed(views::Button* sender, const ui::Event& event) {
-  CaptionButtonId id = static_cast<CaptionButtonId>(sender->id());
+void CaptionBar::HandleButton(CaptionButtonId id) {
+  if (!GetViewByID(static_cast<int>(id))->visible())
+    return;
 
   // If the delegate returns |true| it has handled the event and wishes to
   // prevent default behavior from being performed.
@@ -109,10 +137,4 @@ void CaptionBar::ButtonPressed(views::Button* sender, const ui::Event& event) {
   }
 }
 
-void CaptionBar::SetButtonVisible(CaptionButtonId id, bool visible) {
-  views::View* button = GetViewByID(static_cast<int>(id));
-  if (button)
-    button->SetVisible(visible);
-}
-
 }  // namespace ash

ash/assistant/ui/caption_bar.h

@@ -39,6 +39,7 @@ class CaptionBar : public views::View, views::ButtonListener {
   ~CaptionBar() override;
 
   // views::View:
+  bool AcceleratorPressed(const ui::Accelerator& accelerator) override;
   gfx::Size CalculatePreferredSize() const override;
   int GetHeightForWidth(int width) const override;
 
@@ -52,6 +53,7 @@ class CaptionBar : public views::View, views::ButtonListener {
 
  private:
   void InitLayout();
+  void HandleButton(CaptionButtonId id);
 
   CaptionBarDelegate* delegate_ = nullptr;