Update shelf spacing in Chrome OS according to the MD specs

ash/shelf/shelf_button.cc

Index: ash/shelf/shelf_button.cc
diff --git a/ash/shelf/shelf_button.cc b/ash/shelf/shelf_button.cc
index 70adc8c43270de7649fe2051108f8bbfd8d961f2..591094bf759d39f9da1c0104832da1c372d84e14 100644
--- a/ash/shelf/shelf_button.cc
+++ b/ash/shelf/shelf_button.cc
@@ -509,7 +509,8 @@ void ShelfButton::UpdateBar() {
     Shelf* shelf = shelf_view_->shelf();
     gfx::ImageSkia image;
     if (ash::MaterialDesignController::IsShelfMaterial()) {
-      gfx::Size size(kShelfButtonSize, kShelfSize);
+      gfx::Size size(GetShelfLayoutConstant(SHELF_BUTTON_SIZE),
+                     GetShelfLayoutConstant(SHELF_SIZE));
       gfx::Canvas canvas(size, kIndicatorCanvasScale, true /* is_opaque */);
       PaintIndicatorOnCanvas(&canvas, size);
       image = gfx::ImageSkia(canvas.ExtractImageRep());