Align the base of the shelf's context menu to the top edge of the shelf.

ui/base/ui_base_types.h

Index: ui/base/ui_base_types.h
diff --git a/ui/base/ui_base_types.h b/ui/base/ui_base_types.h
index b07dca26392f981faa4f69dfb406a7a5b34a8f61..2637a29ec936228d2f20635a0d30d51514e35d9b 100644
--- a/ui/base/ui_base_types.h
+++ b/ui/base/ui_base_types.h
@@ -41,13 +41,14 @@ enum ModalType {
 
 // TODO(varunjain): Remove MENU_SOURCE_NONE (crbug.com/250964)
 enum MenuSourceType {
-  MENU_SOURCE_NONE            = 0,
-  MENU_SOURCE_MOUSE           = 1,
-  MENU_SOURCE_KEYBOARD        = 2,
-  MENU_SOURCE_TOUCH           = 3,
-  MENU_SOURCE_TOUCH_EDIT_MENU = 4,
-  MENU_SOURCE_LONG_PRESS      = 5,
-  MENU_SOURCE_LONG_TAP        = 6,
+  MENU_SOURCE_NONE = 0,
+  MENU_SOURCE_MOUSE = 1,
+  MENU_SOURCE_KEYBOARD = 2,
+  MENU_SOURCE_TOUCH = 3,
+  MENU_SOURCE_TOUCH_SIDE_SHELF = 4,

[msw, 2017/05/05 17:34:19]

We probably want to avoid this or make it not shelf-specific (ie. replace
'SHELF' with 'ANCHOR' or 'MENU'); you need to ping ui/base/OWNERS anyway.

+  MENU_SOURCE_TOUCH_EDIT_MENU = 5,
+  MENU_SOURCE_LONG_PRESS = 6,
+  MENU_SOURCE_LONG_TAP = 7,
   MENU_SOURCE_TYPE_LAST = MENU_SOURCE_LONG_TAP
 };