Revert "shelf: Users cannot hide shelf by swipe down in tablet mode anymore."

This reverts commit 4d9e568b.

Reason for revert: <INSERT REASONING HERE>

Original change's description:
> shelf: Users cannot hide shelf by swipe down in tablet mode anymore.
> 
> Test: ash_unittests ShelfLayoutManagerTest.SwipingUpOnShelfInTabletModeForFullscreenAppList
> Bug: 801684
> Change-Id: I142180f8204fc413a46381c45267c7be9463c1ef
> Reviewed-on: https://chromium-review.googlesource.com/868453
> Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
> Commit-Queue: Sammie Quon <sammiequon@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#529507}

TBR=xiyuan@chromium.org,sammiequon@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 801684
Change-Id: I5edae712f04a26eea47811e3f2fd69fd0b9c79d9
Reviewed-on: https://chromium-review.googlesource.com/877160Reviewed-by: Sammie Quon <sammiequon@chromium.org>
Commit-Queue: Sammie Quon <sammiequon@chromium.org>
Cr-Commit-Position: refs/heads/master@{#530701}

ash/shelf/shelf_layout_manager.cc

@@ -86,12 +86,6 @@ bool IsAppListWindow(const aura::Window* window) {
   return parent && parent->id() == kShellWindowId_AppListContainer;
 }
 
-bool IsTabletModeEnabled() {
-  return Shell::Get()
-      ->tablet_mode_controller()
-      ->IsTabletModeWindowManagerEnabled();
-}
-
 }  // namespace
 
 // ShelfLayoutManager::UpdateShelfObserver -------------------------------------
@@ -1106,14 +1100,10 @@ void ShelfLayoutManager::StartGestureDrag(
     launcher_above_shelf_bottom_amount_ =
         shelf_bounds.bottom() - gesture_in_screen.location().y();
   } else {
-    // Only app list drags are allowed in tablet mode.
-    if (IsTabletModeEnabled())
-      return;
-
     // Disable the shelf dragging if the fullscreen app list is opened.
-    if (is_app_list_visible_)
+    if (is_app_list_visible_) {
       return;
-
+    }
     gesture_drag_status_ = GESTURE_DRAG_IN_PROGRESS;
     gesture_drag_auto_hide_state_ = visibility_state() == SHELF_AUTO_HIDE
                                         ? auto_hide_state()
@@ -1141,10 +1131,6 @@ void ShelfLayoutManager::UpdateGestureDrag(
     launcher_above_shelf_bottom_amount_ =
         shelf_bounds.bottom() - gesture_in_screen.location().y();
   } else {
-    // Only app list drags are allowed in tablet mode.
-    if (IsTabletModeEnabled())
-      return;
-
     gesture_drag_amount_ +=
         PrimaryAxisValue(gesture_in_screen.details().scroll_y(),
                          gesture_in_screen.details().scroll_x());
@@ -1154,10 +1140,6 @@ void ShelfLayoutManager::UpdateGestureDrag(
 
 void ShelfLayoutManager::CompleteGestureDrag(
     const ui::GestureEvent& gesture_in_screen) {
-  // Only app list drags are allowed in tablet mode.
-  if (IsTabletModeEnabled())
-    return;
-
   bool should_change = false;
   if (gesture_in_screen.type() == ui::ET_GESTURE_SCROLL_END) {
     // The visibility of the shelf changes only if the shelf was dragged X%
@@ -1230,7 +1212,9 @@ void ShelfLayoutManager::CompleteAppListDrag(
   } else {
     // Snap the app list to corresponding state according to the snapping
     // thresholds.
-    if (IsTabletModeEnabled()) {
+    if (Shell::Get()
+            ->tablet_mode_controller()
+            ->IsTabletModeWindowManagerEnabled()) {
       app_list_state = launcher_above_shelf_bottom_amount_ >
                                kAppListDragSnapToFullscreenThreshold
                            ? AppListState::FULLSCREEN_ALL_APPS

ash/shelf/shelf_layout_manager_unittest.cc

@@ -1503,6 +1503,9 @@ TEST_F(ShelfLayoutManagerTest,
   EXPECT_EQ(SHELF_AUTO_HIDE_BEHAVIOR_NEVER, shelf->auto_hide_behavior());
   EXPECT_EQ(SHELF_VISIBLE, shelf->GetVisibilityState());
 
+  // Note: A window must be visible in order to hide the shelf.
+  views::Widget* widget = CreateTestWidget();
+
   app_list::test::TestAppListPresenter test_app_list_presenter;
   shell->app_list()->SetAppListPresenter(
       test_app_list_presenter.CreateInterfacePtrAndBind());
@@ -1543,12 +1546,35 @@ TEST_F(ShelfLayoutManagerTest,
   EXPECT_EQ(app_list::mojom::AppListState::CLOSED,
             test_app_list_presenter.app_list_state());
 
-  // Swiping down on the shelf should do nothing in tablet mode.
+  // Swiping down on the shelf should hide it.
   end = start + delta;
   generator.GestureScrollSequence(start, end, kTimeDelta, kNumScrollSteps);
-  EXPECT_EQ(SHELF_ALIGNMENT_BOTTOM, shelf->alignment());
-  EXPECT_EQ(SHELF_AUTO_HIDE_BEHAVIOR_NEVER, shelf->auto_hide_behavior());
+  EXPECT_EQ(SHELF_AUTO_HIDE, shelf->GetVisibilityState());
+  EXPECT_EQ(SHELF_AUTO_HIDE_HIDDEN, shelf->GetAutoHideState());
+  EXPECT_EQ(SHELF_AUTO_HIDE_BEHAVIOR_ALWAYS, shelf->auto_hide_behavior());
+
+  // Swiping up should show the shelf but not the app list if shelf is hidden.
+  generator.GestureScrollSequence(end, start, kTimeDelta, kNumScrollSteps);
+  RunAllPendingInMessageLoop();
   EXPECT_EQ(SHELF_VISIBLE, shelf->GetVisibilityState());
+  EXPECT_EQ(SHELF_AUTO_HIDE_BEHAVIOR_NEVER, shelf->auto_hide_behavior());
+  EXPECT_EQ(2u, test_app_list_presenter.show_count());
+  EXPECT_GE(test_app_list_presenter.set_y_position_count(), 1u);
+  EXPECT_EQ(app_list::mojom::AppListState::CLOSED,
+            test_app_list_presenter.app_list_state());
+
+  // Swiping down should hide the shelf.
+  generator.GestureScrollSequence(start, end, kTimeDelta, kNumScrollSteps);
+  EXPECT_EQ(SHELF_AUTO_HIDE, shelf->GetVisibilityState());
+  EXPECT_EQ(SHELF_AUTO_HIDE_HIDDEN, shelf->GetAutoHideState());
+  EXPECT_EQ(SHELF_AUTO_HIDE_BEHAVIOR_ALWAYS, shelf->auto_hide_behavior());
+
+  // Minimize the visible window, the shelf should be shown if there are no
+  // visible windows, even in auto-hide mode.
+  widget->Minimize();
+  EXPECT_EQ(SHELF_AUTO_HIDE, shelf->GetVisibilityState());
+  EXPECT_EQ(SHELF_AUTO_HIDE_SHOWN, shelf->GetAutoHideState());
+  EXPECT_EQ(SHELF_AUTO_HIDE_BEHAVIOR_ALWAYS, shelf->auto_hide_behavior());
 
   // Swiping up on the shelf in this state should open the app list.
   delta.set_y(ShelfLayoutManager::kAppListDragSnapToFullscreenThreshold + 10);