Moves maintaining ShellObservers back to Shell

ash/common/wm/panels/panel_frame_view.cc

Index: ash/common/wm/panels/panel_frame_view.cc
diff --git a/ash/common/wm/panels/panel_frame_view.cc b/ash/common/wm/panels/panel_frame_view.cc
index 67ef90cf79e7df702b80d7bdecdc5de0f4b5561f..c6546d7da505effa7d7ff11d13a2e01fb682757e 100644
--- a/ash/common/wm/panels/panel_frame_view.cc
+++ b/ash/common/wm/panels/panel_frame_view.cc
@@ -7,8 +7,8 @@
 #include "ash/common/frame/caption_buttons/frame_caption_button_container_view.h"
 #include "ash/common/frame/default_header_painter.h"
 #include "ash/common/frame/frame_border_hit_test.h"
-#include "ash/common/wm_shell.h"
 #include "ash/common/wm_window.h"
+#include "ash/shell.h"
 #include "ui/aura/client/aura_constants.h"
 #include "ui/aura/window.h"
 #include "ui/base/hit_test.h"
@@ -28,11 +28,11 @@ PanelFrameView::PanelFrameView(views::Widget* frame, FrameType frame_type)
   DCHECK(!frame_->widget_delegate()->CanMaximize());
   if (frame_type != FRAME_NONE)
     InitHeaderPainter();
-  WmShell::Get()->AddShellObserver(this);
+  Shell::GetInstance()->AddShellObserver(this);
 }
 
 PanelFrameView::~PanelFrameView() {
-  WmShell::Get()->RemoveShellObserver(this);
+  Shell::GetInstance()->RemoveShellObserver(this);
 }
 
 void PanelFrameView::SetFrameColors(SkColor active_frame_color,