Update shelf spacing in Chrome OS according to the MD specs

ash/shelf/shelf_constants.h

Index: ash/shelf/shelf_constants.h
diff --git a/ash/shelf/shelf_constants.h b/ash/shelf/shelf_constants.h
index d7f0825b7394263afdec8f6f8952ef8c6e7f7a03..6c99603093c5ae00599d8c479df31a4b4f5a4913 100644
--- a/ash/shelf/shelf_constants.h
+++ b/ash/shelf/shelf_constants.h
@@ -9,19 +9,34 @@
 
 namespace ash {
 
+enum ShelfLayoutConstant {
+  // Size of the shelf when visible (height when the shelf is horizontal).

[bruthig, 2016/05/25 20:24:52]

nit: Can you add 'and width when the shelf is vertical'

[yiyix, 2016/06/02 03:54:53]

Done.

+  SHELF_SIZE,
+
+  // Size of the space between buttons on the shelf.
+  SHELF_BUTTON_SPACING,
+
+  // Size allocated for each button on the shelf.
+  SHELF_BUTTON_SIZE
+};
+
+ASH_EXPORT int GetShelfLayoutConstant(ShelfLayoutConstant constant);
+
 // Invalid image resource id used for ShelfItemDetails.
 extern const int kInvalidImageResourceID;
 
-const int kInvalidShelfID = 0;
+// We reserve a small area on the edge of the workspace area to ensure that
+// the resize handle at the edge of the window can be hit.
+extern const int kWorkspaceAreaVisibleInset;

[bruthig, 2016/05/25 20:24:52]

Please wrap these three constants in a class.  'kAutoHideSize' is too general of
a variable name to be in the ash namespace.

It might make sense to move the GetShelfLayoutConstants() function to this class
too, i.e.  ShelfLayoutConstants::Get(ShelfLayoutConstant).

[tdanderson, 2016/05/26 22:55:56]

For the purposes of this CL, I would actually refrain from touching these three
constants at all; they have the same values in both pre-MD and MD.

[yiyix, 2016/06/02 03:54:53]

I wanted to move most of the shelf property related constants into this
shelf_constansts.h file. So I moved them here.

 
-// Size of the shelf when visible (height when the shelf is horizontal).
-ASH_EXPORT extern const int kShelfSize;
+// When autohidden we extend the touch hit target onto the screen so that the
+// user can drag the shelf out.
+extern const int kWorkspaceAreaAutoHideInset;
 
-// Size of the space between buttons on the shelf.
-ASH_EXPORT extern const int kShelfButtonSpacing;
+// Size of the shelf when auto-hidden.
+ASH_EXPORT extern const int kAutoHideSize;
 
-// Size allocated for each button on the shelf.
-ASH_EXPORT extern const int kShelfButtonSize;
+const int kInvalidShelfID = 0;
 
 // The direction of the focus cycling.
 enum CycleDirection {