Add tooltip to close button in app info dialog.

ui/views/bubble/bubble_frame_view.cc

Index: ui/views/bubble/bubble_frame_view.cc
diff --git a/ui/views/bubble/bubble_frame_view.cc b/ui/views/bubble/bubble_frame_view.cc
index 599d5965f2880ab57ca9218144a0cf0877aa48cd..dff1e993c38982f0e6869eebfe6b7b7a9b7b85c6 100644
--- a/ui/views/bubble/bubble_frame_view.cc
+++ b/ui/views/bubble/bubble_frame_view.cc
@@ -7,12 +7,14 @@
 #include <algorithm>
 
 #include "ui/base/hit_test.h"
+#include "ui/base/l10n/l10n_util.h"
 #include "ui/base/resource/resource_bundle.h"
 #include "ui/gfx/path.h"
 #include "ui/gfx/screen.h"
 #include "ui/gfx/skia_util.h"
 #include "ui/native_theme/native_theme.h"
 #include "ui/resources/grit/ui_resources.h"
+#include "ui/strings/grit/ui_strings.h"
 #include "ui/views/bubble/bubble_border.h"
 #include "ui/views/controls/button/label_button.h"
 #include "ui/views/controls/image_view.h"
@@ -103,6 +105,7 @@ LabelButton* BubbleFrameView::CreateCloseButton(ButtonListener* listener) {
                   *rb.GetImageNamed(IDR_CLOSE_DIALOG_P).ToImageSkia());
   close->SetBorder(nullptr);
   close->SetSize(close->GetPreferredSize());
+  close->SetTooltipText(l10n_util::GetStringUTF16(IDS_APP_CLOSE));
   return close;
 }