overview gesture: No drag above the shelf.

Do not allow the drag if the drag position starts above the shelf.

Bug: 997885
Change-Id: Ifd5619cd28d96de889c28cd2c51fe67586224783
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1880079Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Xiaoqian Dai <xdai@chromium.org>
Cr-Commit-Position: refs/heads/master@{#709618}

ash/shelf/shelf_layout_manager.cc

@@ -2352,6 +2352,12 @@ void ShelfLayoutManager::MaybeStartDragWindowFromShelf(
     return;
   }
 
+  // If the start location is above the shelf (e.g., on the extended hotseat),
+  // do not allow the drag.
+  const gfx::Rect shelf_bounds = GetVisibleShelfBounds();
+  if (event_in_screen.location().y() < shelf_bounds.y())
+    return;
+
   aura::Window* window =
       GetWindowForDragToHomeOrOverview(event_in_screen.location());
   if (!window)

ash/shelf/shelf_layout_manager_unittest.cc

@@ -3905,6 +3905,24 @@ TEST_F(ShelfLayoutManagerWindowDraggingTest, NoOpForHiddenShelf) {
   EndScroll(/*is_fling=*/false, 0.f);
 }
 
+TEST_F(ShelfLayoutManagerWindowDraggingTest, NoOpIfDragStartsAboveShelf) {
+  std::unique_ptr<aura::Window> window =
+      AshTestBase::CreateTestWindow(gfx::Rect(0, 0, 400, 400));
+  wm::ActivateWindow(window.get());
+
+  Shelf* shelf = GetPrimaryShelf();
+  shelf->SetAutoHideBehavior(SHELF_AUTO_HIDE_BEHAVIOR_ALWAYS);
+  SwipeUpOnShelf();
+  EXPECT_EQ(SHELF_AUTO_HIDE_SHOWN, shelf->GetAutoHideState());
+  EXPECT_EQ(HotseatState::kExtended, GetShelfLayoutManager()->hotseat_state());
+
+  gfx::Rect hotseat_bounds =
+      GetShelfWidget()->hotseat_widget()->GetWindowBoundsInScreen();
+  StartScroll(hotseat_bounds.CenterPoint());
+  EXPECT_FALSE(GetShelfLayoutManager()->window_drag_controller_for_testing());
+  EndScroll(/*is_fling=*/false, 0.f);
+}
+
 class ShelfLayoutManagerKeyboardTest : public AshTestBase {
  public:
   ShelfLayoutManagerKeyboardTest() = default;