Update shelf spacing in Chrome OS according to the MD specs

ash/system/tray/tray_constants.h

Index: ash/system/tray/tray_constants.h
diff --git a/ash/system/tray/tray_constants.h b/ash/system/tray/tray_constants.h
index fa633cffd97a29fdd7d73e22c3b16470cf766e92..b971eb4443ad0e55515f9599f81d721b164a1c95 100644
--- a/ash/system/tray/tray_constants.h
+++ b/ash/system/tray/tray_constants.h
@@ -22,7 +22,15 @@ extern const int kBubblePaddingHorizontalSide;
 extern const int kBubblePaddingVerticalBottom;
 extern const int kBubblePaddingVerticalSide;
 
-extern const int kPaddingFromEdgeOfShelf;
+extern const int kAdjustBackgroundPadding;
+enum ShelfStatusAreaInset {
+  // Padding between icons in the status tray area.
+  TRAY_SPACING,
+
+  // Padding between the edge of shelf and the item in status tray area.
+  PADDING_FROM_EDGE_OF_SHELF,
+};
+
 extern const int kTrayBubbleAnchorTopInsetBottomAnchor;
 
 extern const int kTrayImageItemHorizontalPaddingBottomAlignment;
@@ -76,9 +84,14 @@ extern const int kTrayNotificationContentsWidth;
 extern const int kTrayAvatarCornerRadius;
 extern const int kTrayAvatarSize;
 
-extern const int kTraySpacing;
+extern const int kMessageCenterBubblePadding;
 extern const int kShelfItemHeight;
 
+// Index of the overview button in the status area.
+extern const int kOverviewButtonIndex;
+
+int GetTrayConstant(ShelfStatusAreaInset constant);
+
 namespace test {
 const int kSettingsTrayItemViewId = 10000;
 const int kAccessibilityTrayItemViewId = 10001;