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

ash/shelf/shelf_view.cc

Index: ash/shelf/shelf_view.cc
diff --git a/ash/shelf/shelf_view.cc b/ash/shelf/shelf_view.cc
index d2de17bb6a394191b941af37f8896dd32f8b07f3..0d052d712d0cb69dbf76a6e415bf5d1dd10ab2fc 100644
--- a/ash/shelf/shelf_view.cc
+++ b/ash/shelf/shelf_view.cc
@@ -11,6 +11,7 @@
 #include "ash/drag_drop/drag_image_view.h"
 #include "ash/public/cpp/shelf_item_delegate.h"
 #include "ash/scoped_root_window_for_new_windows.h"
+#include "ash/screen_util.h"
 #include "ash/shelf/app_list_button.h"
 #include "ash/shelf/overflow_bubble.h"
 #include "ash/shelf/overflow_bubble_view.h"
@@ -1639,11 +1640,32 @@ void ShelfView::AfterItemSelected(
 void ShelfView::ShowContextMenuForView(views::View* source,
                                        const gfx::Point& point,
                                        ui::MenuSourceType source_type) {
+  // Align the context menu to the edge of the shelf.
+  aura::Window* shelf_window = shelf_widget_->GetNativeWindow();
+  gfx::Rect shelf_bounds =
+      is_overflow_mode()
+          ? (owner_overflow_bubble_->bubble_view()->GetBubbleBounds())
+          : (ScreenUtil::GetDisplayBoundsWithShelf(shelf_window));
+
+  gfx::Point context_menu_point;
+  switch (wm_shelf_->GetAlignment()) {
+    case SHELF_ALIGNMENT_BOTTOM:
+    case SHELF_ALIGNMENT_BOTTOM_LOCKED:
+      context_menu_point.SetPoint(point.x(),
+                                  shelf_bounds.bottom() - kShelfSize);
+      break;
+    case SHELF_ALIGNMENT_LEFT:
+      context_menu_point.SetPoint(shelf_bounds.x() + kShelfSize, point.y());
+      break;
+    case SHELF_ALIGNMENT_RIGHT:
+      context_menu_point.SetPoint(shelf_bounds.right() - kShelfSize, point.y());
+      break;
+  }
   last_pressed_index_ = -1;
 
   const ShelfItem* item = ShelfItemForView(source);
   if (!item) {
-    ShellPort::Get()->ShowContextMenu(point, source_type);
+    ShellPort::Get()->ShowContextMenu(context_menu_point, source_type);
     return;
   }
 
@@ -1653,8 +1675,8 @@ void ShelfView::ShowContextMenuForView(views::View* source,
     return;
 
   context_menu_id_ = item ? item->id : ShelfID();
-  ShowMenu(std::move(context_menu_model), source, point, true, source_type,
-           nullptr);
+  ShowMenu(std::move(context_menu_model), source, context_menu_point, true,
+           source_type, nullptr);
 }
 
 void ShelfView::ShowMenu(std::unique_ptr<ui::MenuModel> menu_model,
@@ -1709,6 +1731,14 @@ void ShelfView::ShowMenu(std::unique_ptr<ui::MenuModel> menu_model,
     }
   }
 
+  // Distinguish the touch events that triggered on the bottom shelf or
+  // left / right shelf. Since they should have different |MenuAnchorPosition|.
+  if (source_type == ui::MENU_SOURCE_TOUCH) {
+    if (wm_shelf_->IsHorizontalAlignment())
+      source_type = ui::MENU_SOURCE_TOUCH_BOTTOM_ANCHOR;
+    else
+      source_type = ui::MENU_SOURCE_TOUCH_SIDE_ANCHOR;
+  }
   // NOTE: if you convert to HAS_MNEMONICS be sure to update menu building code.
   launcher_menu_runner_->RunMenuAt(source->GetWidget(), nullptr, anchor,
                                    menu_alignment, source_type);
@@ -1795,7 +1825,7 @@ bool ShelfView::CanPrepareForDrag(Pointer pointer,
     return false;
   }
 
-  // Touch dragging only begins after a dealy from the press event. This
+  // Touch dragging only begins after a delay from the press event. This
   // prevents accidental dragging on swipe or scroll gestures.
   if (pointer == TOUCH &&
       (base::TimeTicks::Now() - touch_press_time_) <