Add new UMA stats to get a handle on Downloads UI Usage

chrome/browser/ui/views/download/download_shelf_view.cc

Index: chrome/browser/ui/views/download/download_shelf_view.cc
diff --git a/chrome/browser/ui/views/download/download_shelf_view.cc b/chrome/browser/ui/views/download/download_shelf_view.cc
index f60424a4e1b14b7c3968ceeffb6c5f5a96cf0c69..5877e97769666a71c1682cc198934c5f01d75da1 100644
--- a/chrome/browser/ui/views/download/download_shelf_view.cc
+++ b/chrome/browser/ui/views/download/download_shelf_view.cc
@@ -15,6 +15,7 @@
 #include "chrome/browser/ui/views/download/download_item_view.h"
 #include "chrome/browser/ui/views/frame/browser_view.h"
 #include "content/browser/download/download_item.h"
+#include "content/browser/download/download_stats.h"
 #include "content/browser/download/download_manager.h"
 #include "content/browser/tab_contents/navigation_entry.h"
 #include "grit/generated_resources.h"
@@ -383,6 +384,7 @@ void DownloadShelfView::Show() {
 }
 
 void DownloadShelfView::Close() {
+  download_stats::RecordShelfSize(download_views_.size());
   parent_->SetDownloadShelfVisible(false);
   shelf_animation_->Hide();
 }