mash: Move ownership of ShelfDelegate to WmShell

ash/metrics/user_metrics_recorder.cc

Index: ash/metrics/user_metrics_recorder.cc
diff --git a/ash/metrics/user_metrics_recorder.cc b/ash/metrics/user_metrics_recorder.cc
index 8577b9992b07ac03017d380d803ae6717bc47d6b..f475e96afb7fab13955ffaa615ea04295cab1b0e 100644
--- a/ash/metrics/user_metrics_recorder.cc
+++ b/ash/metrics/user_metrics_recorder.cc
@@ -5,6 +5,7 @@
 #include "ash/metrics/user_metrics_recorder.h"
 
 #include "ash/common/session/session_state_delegate.h"
+#include "ash/common/shelf/shelf_delegate.h"
 #include "ash/common/shelf/shelf_item_types.h"
 #include "ash/common/shelf/shelf_model.h"
 #include "ash/common/shell_window_ids.h"
@@ -13,7 +14,6 @@
 #include "ash/common/wm_shell.h"
 #include "ash/metrics/desktop_task_switch_metric_recorder.h"
 #include "ash/shelf/shelf.h"
-#include "ash/shelf/shelf_delegate.h"
 #include "ash/shelf/shelf_view.h"
 #include "ash/shell.h"
 #include "ash/wm/window_state_aura.h"
@@ -157,7 +157,7 @@ int GetNumVisibleWindowsInPrimaryDisplay() {
 
 // Records the number of items in the shelf as an UMA statistic.
 void RecordShelfItemCounts() {
-  ShelfDelegate* shelf_delegate = Shell::GetInstance()->GetShelfDelegate();
+  ShelfDelegate* shelf_delegate = WmShell::Get()->shelf_delegate();

[msw, 2016/07/23 00:02:36]

Couldn't this now be null if no shelves have called CreateShelfDelegate? The old
accessor would lazily create the shelf delegate if needed. ditto elsewhere

[James Cook, 2016/07/23 00:38:03]

Added DCHECKs.

I thought the lazy construction before was confusing. I could not tell by
reading the code when the object was created. If you think it's better to lazily
create the delegate then I'm happy to move it into the getter.

   int pinned_item_count = 0;
   int unpinned_item_count = 0;