Add basic Chrome interaction with the mash shelf.

mash/shelf/public/interfaces/shelf.mojom

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+module mash.shelf.mojom;
+
+import "skia/public/interfaces/bitmap.mojom";
+
+// The Shelf interface allows clients (eg. Chrome) to control the mash shelf.
+interface Shelf {
+  AddObserver(ShelfObserver observer);
+
+  SetAlignment(Alignment alignment);
+  SetAutoHideBehavior(AutoHideBehavior auto_hide);
+
+  AddItem(ShelfItem item, ShelfItemDelegate delegate);
+  RemoveItem(string id);
+};
+
+// ShelfObserver is notified on shelf changes; used to persist profile settings.
+interface ShelfObserver {

[sky, 2016/04/06 02:57:45]

When the observer is added seems like you should call OnAlignment/OnAutoHide*.
Otherwise, how does the observer know the state?

[msw, 2016/04/07 20:34:57]

Done. FYI: we now rely on the ordering of (1) chrome setting the initial values
from prefs, and then (2) adding itself as an observer (so it doesn't get
notified of the default/uninitialized ash state and try to save that as a user
preference). Luckily that's how ChromeMashShelfController::Init works already.

[sky, 2016/04/07 22:02:46]

Be sure and document this.

+  OnAlignmentChanged(Alignment alignment);
+  OnAutoHideBehaviorChanged(AutoHideBehavior auto_hide);
+};
+
+// ShelfItemDelegate handles command execution and observes shelf item changes.
+interface ShelfItemDelegate {

[sky, 2016/04/06 02:57:45]

Why do you need 'id' in each of these functions? Isn't the delegate associated
with one and only one item, whose id won't change?

[sky, 2016/04/06 02:57:45]

I'm nervous that all the delegates are different pipes. An implication of that
is ordering is not guaranteed. Would it make sense to have all the delegates
associated with the shelf, and perhaps the ShelfObserver associated with the
shelf too?

[msw, 2016/04/07 20:34:57]

I had planned that a single ShelfItemDelegate might exist for multiple shelf
items, but that's probably not necessary and not how the existing
LauncherItemController works, so I changed this around.

[msw, 2016/04/07 20:34:58]

OKay, I associated observers and item delegates with the shelf controller
interface. I had to add AssociatedInterfacePtrSet (copypasta of
InterfacePtrSet); hope it's all right!

+  // Called on invocation of a shelf item's context menu command.
+  ExecuteCommand(string id, uint32 command_id, int32 event_flags);
+
+  // Called when a pinned shelf item is unpinned.
+  ItemRemoved(string id);

[sky, 2016/04/06 02:57:45]

If this is called when the item is unpinned can it be called ItemUnpinned? Might
the item become pinned again?

[msw, 2016/04/07 20:34:57]

Yes and good call.

+
+  // Called when a pinned shelf item is reordered.
+  ItemReordered(string id, uint32 order);

[sky, 2016/04/06 02:57:45]

Document what 'order' means. 

[msw, 2016/04/07 20:34:57]

Done.

+};
+
+// These values match ash::ShelfAlignment.
+enum Alignment { BOTTOM, LEFT, RIGHT, };
+
+// These values match ash::ShelfAutoHideBehavior.
+enum AutoHideBehavior { ALWAYS, NEVER, HIDDEN, };
+
+// ContextMenuItems may be used to supplement ash shelf item context menus.
+struct ContextMenuItem {
+  enum Type { ITEM, CHECK, RADIO, SEPARATOR, SUBMENU };
+
+  Type type;
+  uint32 command_id;
+  string? label;
+  array<ContextMenuItem>? submenu;
+  bool enabled;
+  bool checked;
+  uint32 radio_group_id;
+};
+
+// ShelfItem contains the basic fields needed to pin shortcut items.
+struct ShelfItem {
+  // An id, used to correlate windows and shortcuts (eg. 'exe:chrome').
+  string id;
+
+  // A title, used for tooltips, etc. (eg. 'Chrome').
+  string title;
+
+  // An icon image Bitmap, shown on the shelf.
+  skia.mojom.Bitmap image;
+
+  // Additional context menu items (eg. 'New Incognito Window').
+  array<ContextMenuItem>? context_menu_items;
+};