Update shelf spacing in Chrome OS according to the MD specs

ash/common/system/tray/tray_constants.h

Index: ash/common/system/tray/tray_constants.h
diff --git a/ash/common/system/tray/tray_constants.h b/ash/common/system/tray/tray_constants.h
index f6c9c16e1a61bdb604ee67dad85f59e69b9da496..29952dce42e0d072f504e492fff521e957fdf47b 100644
--- a/ash/common/system/tray/tray_constants.h
+++ b/ash/common/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.

[tdanderson, 2016/06/10 22:54:42]

nit: icons -> items

[yiyix, 2016/06/13 18:43:54]

Done.

+  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;
@@ -76,8 +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;
+extern const int kShelfItemSizeMD;
+
+// Index of the overview button in the status area.
+extern const int kOverviewButtonIndex;
+
+int GetTrayConstant(ShelfStatusAreaInset constant);
 
 namespace test {
 const int kSettingsTrayItemViewId = 10000;