ash: Explicitly teach various components about ShelfLayoutManager.

ash/shelf/overflow_button.h

Index: ash/shelf/overflow_button.h
diff --git a/ash/shelf/overflow_button.h b/ash/shelf/overflow_button.h
index 04f01faee5e0eff93ff8f68002ef4ad7f6f9c4d5..23270ddbbe7e4a6ab6572aed2bbe88d270521019 100644
--- a/ash/shelf/overflow_button.h
+++ b/ash/shelf/overflow_button.h
@@ -13,10 +13,12 @@
 
 namespace ash {
 
+class ShelfLayoutManager;
+
 // Shelf overflow chevron button.
 class OverflowButton : public views::CustomButton {
  public:
-  explicit OverflowButton(views::ButtonListener* listener);
+  OverflowButton(views::ButtonListener* listener, ShelfLayoutManager* shelf);
   ~OverflowButton() override;
 
   void OnShelfAlignmentChanged();
@@ -33,6 +35,7 @@ class OverflowButton : public views::CustomButton {
   gfx::ImageSkia right_image_;
   // Bottom image is owned by the resource bundle.
   const gfx::ImageSkia* bottom_image_;
+  ShelfLayoutManager* shelf_;
 
   DISALLOW_COPY_AND_ASSIGN(OverflowButton);
 };