Collects stats on how user interacts with the bubble.

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 384c4fa46a8ddb4cbe788c33d71d769e75493e33..3f75d0591f9b76ee88d11f99dfa58be6db8e44f6 100644
--- a/ui/views/bubble/bubble_frame_view.cc
+++ b/ui/views/bubble/bubble_frame_view.cc
@@ -6,6 +6,7 @@
 
 #include <algorithm>
 
+#include "base/bind.h"
 #include "grit/ui_resources.h"
 #include "ui/base/hit_test.h"
 #include "ui/base/resource/resource_bundle.h"
@@ -50,6 +51,9 @@ int GetOffScreenLength(const gfx::Rect& available_bounds,
          std::max(0, window_bounds.right() - available_bounds.right());
 }
 
+// The default value for callback_before_close_.
+void EmptyCallback() {}
+
 }  // namespace
 
 namespace views {
@@ -68,7 +72,8 @@ BubbleFrameView::BubbleFrameView(const gfx::Insets& content_margins)
       content_margins_(content_margins),
       title_(NULL),
       close_(NULL),
-      titlebar_extra_view_(NULL) {
+      titlebar_extra_view_(NULL),
+      callback_before_close_(base::Bind(&EmptyCallback)) {

[Alexei Svitkine (slow), 2014/07/02 15:07:26]

I think you can initialize it with the default ctor and then just do:

if (!callback_before_close_.is_null())
  callback_before_close_.Run();

[yao, 2014/07/07 17:47:45]

Done.

   ui::ResourceBundle& rb = ui::ResourceBundle::GetSharedInstance();
   title_ = new Label(base::string16(),
                      rb.GetFontList(ui::ResourceBundle::MediumFont));
@@ -238,8 +243,10 @@ void BubbleFrameView::OnNativeThemeChanged(const ui::NativeTheme* theme) {
 }
 
 void BubbleFrameView::ButtonPressed(Button* sender, const ui::Event& event) {
-  if (sender == close_)
+  if (sender == close_) {
+    callback_before_close_.Run();
     GetWidget()->Close();
+  }
 }
 
 void BubbleFrameView::SetBubbleBorder(scoped_ptr<BubbleBorder> border) {