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

chrome/browser/ui/cocoa/download/download_shelf_controller.mm

Index: chrome/browser/ui/cocoa/download/download_shelf_controller.mm
diff --git a/chrome/browser/ui/cocoa/download/download_shelf_controller.mm b/chrome/browser/ui/cocoa/download/download_shelf_controller.mm
index fb69b913340d9eaddedf312fc7cb97566db84aa4..03a666c9c6e470c2a01523de5b42c23d6c43e97d 100644
--- a/chrome/browser/ui/cocoa/download/download_shelf_controller.mm
+++ b/chrome/browser/ui/cocoa/download/download_shelf_controller.mm
@@ -20,6 +20,7 @@
 #import "chrome/browser/ui/cocoa/presentation_mode_controller.h"
 #include "content/browser/download/download_item.h"
 #include "content/browser/download/download_manager.h"
+#include "content/browser/download/download_stats.h"
 #import "third_party/GTM/AppKit/GTMNSAnimation+Duration.h"
 #include "ui/base/l10n/l10n_util.h"
 
@@ -240,6 +241,22 @@ const NSSize kHoverCloseButtonDefaultSize = { 16, 16 };
 - (void)hide:(id)sender {
   [self cancelAutoCloseAndRemoveTrackingArea];
 
+  download_stats::RecordShelfSize([downloadItemControllers_ count]);
+
+  int numPending = 0;
+  NSUInteger i = 0;
+  while (i < [downloadItemControllers_ count]) {
+    DownloadItemController* itemController =
+        [downloadItemControllers_ objectAtIndex:i];
+    DownloadItem* download = [itemController download];
+    bool isTransferDone = download->IsComplete() ||
+                          download->IsCancelled() ||
+                          download->IsInterrupted();
+    if (!isTransferDone)
+      ++numPending;
+  }
+  download_stats::RecordShelfPendingSize(numPending);
+
   // If |sender| isn't nil, then we're being closed from the UI by the user and
   // we need to tell our shelf implementation to close. Otherwise, we're being
   // closed programmatically by our shelf implementation.