mash: Convert all of //ash/system to use WmShelf

ash/test/ash_test_base.h

Index: ash/test/ash_test_base.h
diff --git a/ash/test/ash_test_base.h b/ash/test/ash_test_base.h
index 8a7bd7ccf04827324aef1a0134e49dd952dc83f5..68b30e0a7c46232d906328e129b39a088f5892d0 100644
--- a/ash/test/ash_test_base.h
+++ b/ash/test/ash_test_base.h
@@ -43,7 +43,6 @@ class WindowDelegate;
 namespace ash {
 class DisplayManager;
 class SystemTray;
-class WmShelf;
 
 namespace test {
 
@@ -121,9 +120,6 @@ class AshTestBase : public testing::Test {
   // Proxy to AshTestHelper::SupportsHostWindowResize().
   static bool SupportsHostWindowResize();
 
-  // Returns the WmShelf for the primary display.
-  static WmShelf* GetPrimaryShelf();
-
   void set_start_session(bool start_session) { start_session_ = start_session; }
 
   AshTestHelper* ash_test_helper() { return ash_test_helper_.get(); }