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

ui/views/controls/menu/menu_controller.cc

 // Copyright (c) 2012 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.
 
 #include "ui/views/controls/menu/menu_controller.h"
 
 #include "base/i18n/case_conversion.h"
 #include "base/i18n/rtl.h"
 #include "base/macros.h"
 #include "base/strings/utf_string_conversions.h"
@@ skipping 55 matching lines @@
 // the menu item on the subsequent mouse up. To prevent this, we add the
 // following delay before the user is able to select an item.
 int menu_selection_hold_time_ms = kMinimumMsPressedToActivate;
 
 // Period of the scroll timer (in milliseconds).
 const int kScrollTimerMS = 30;
 
 // Amount of time from when the drop exits the menu and the menu is hidden.
 const int kCloseOnExitTime = 1200;
 
-// If a context menu is invoked by touch, we shift the menu by this offset so
-// that the finger does not obscure the menu.
-const int kCenteredContextMenuYOffset = -15;

[minch1, 2017/05/04 16:44:15]

Sorry, not quite sure about here. This is not needed by the shelf context menu
now. But |MENU_ANCHOR_BOTTOMCENTER| is also used by |ToolkitDelegateViews|. I am
not sure whether it is ok to remove this variable here directly? msw@, what's
your opinion?

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

This seems wrong, it'll change the positioning of all touch menus, not just the
shelf ones. Perhaps we should be using MENU_ANCHOR_BUBBLE_* for shelf menus?
(ShelfView::ShowMenu is already the only user of those MENU_ANCHOR_BUBBLE_*
values). Or, perhaps (1) add yet another anchor that works like BOTTOMCENTER but
doesn't apply the offset, or (2) make the shelf apply the inverse of this offset
when constructing the menu...

-
 // The spacing offset for the bubble tip.
 const int kBubbleTipSizeLeftRight = 12;
 const int kBubbleTipSizeTopBottom = 11;
 
 // The maximum distance (in DIPS) that the mouse can be moved before it should
 // trigger a mouse menu item activation (regardless of how long the menu has
 // been showing).
 const float kMaximumLengthMovedToActivate = 4.0f;
 
 // Returns true if the mnemonic of |menu| matches key.
@@ skipping 1854 matching lines @@
     if (menu_config.offset_context_menus && state_.context_menu)
       x += 1;
 
     y = state_.initial_bounds.bottom();
     if (state_.anchor == MENU_ANCHOR_TOPRIGHT) {
       x = x + state_.initial_bounds.width() - pref.width();
       if (menu_config.offset_context_menus && state_.context_menu)
         x -= 1;
     } else if (state_.anchor == MENU_ANCHOR_BOTTOMCENTER) {
       x = x - (pref.width() - state_.initial_bounds.width()) / 2;
-      if (pref.height() >
-          state_.initial_bounds.y() + kCenteredContextMenuYOffset) {
-        // Menu does not fit above the anchor. We move it to below.
-        y = state_.initial_bounds.y() - kCenteredContextMenuYOffset;
-      } else {
-        y = std::max(0, state_.initial_bounds.y() - pref.height()) +
-            kCenteredContextMenuYOffset;
-      }
+      // If menu does not fit above the anchor. We move it to below.

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

nit: "Place the menu below the anchor if it does not fit above."

+      y = pref.height() > state_.initial_bounds.y()
+              ? state_.initial_bounds.y()
+              : (state_.initial_bounds.y() - pref.height());
+    } else if (state_.anchor == MENU_ANCHOR_SIDECENTER) {
+      y = y - (pref.height() - state_.initial_bounds.height()) / 2;

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

nit: y -= (or += with subtraction reversed might be a little simpler?)

     }
 
     if (!state_.monitor_bounds.IsEmpty() &&
         y + pref.height() > state_.monitor_bounds.bottom()) {
       // The menu doesn't fit fully below the button on the screen. The menu
       // position with respect to the bounds will be preserved if it has
       // already been drawn. When the requested positioning is below the bounds
       // it will shrink the menu to make it fit below.
       // If the requested positioning is best fit, it will first try to fit the
       // menu below. If that does not fit it will try to place it above. If
@@ skipping 738 matching lines @@
   if (hot_button_)
     hot_button_->SetHotTracked(false);
   hot_button_ = hot_button;
   if (hot_button) {
     hot_button->SetHotTracked(true);
     hot_button->NotifyAccessibilityEvent(ui::AX_EVENT_SELECTION, true);
   }
 }
 
 }  // namespace views