Fix freezing app list after duplicate swipe from bezel

Background:
Two times of continuous swipe up from bezel breaks scroll event in app
list because second scroll begin event will be consumed by shelf layout
manager, which makes subsequent scroll events go into shelf layout
manager instead of app list.

Changes:
Avoid consuming the scroll event when launcher is visible.

Bug: 896934
Change-Id: I46c9ad8f43a15160b890e5a6d4485dbb3e6bed3d
Reviewed-on: https://chromium-review.googlesource.com/c/1291788Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Weidong Guo <weidongg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#601237}

ash/shelf/shelf_layout_manager.cc

@@ -386,10 +386,8 @@ bool ShelfLayoutManager::ProcessGestureEvent(
   if (IsShelfHiddenForFullscreen())
     return false;
 
-  if (event_in_screen.type() == ui::ET_GESTURE_SCROLL_BEGIN) {
-    StartGestureDrag(event_in_screen);
-    return true;
-  }
+  if (event_in_screen.type() == ui::ET_GESTURE_SCROLL_BEGIN)
+    return StartGestureDrag(event_in_screen);
 
   if (gesture_drag_status_ != GESTURE_DRAG_IN_PROGRESS &&
       gesture_drag_status_ != GESTURE_DRAG_APPLIST_IN_PROGRESS) {
@@ -1191,7 +1189,7 @@ bool ShelfLayoutManager::ShouldBlurShelfBackground() {
 ////////////////////////////////////////////////////////////////////////////////
 // ShelfLayoutManager, Gesture functions:
 
-void ShelfLayoutManager::StartGestureDrag(
+bool ShelfLayoutManager::StartGestureDrag(
     const ui::GestureEvent& gesture_in_screen) {
   if (CanStartFullscreenAppListDrag(
           gesture_in_screen.details().scroll_y_hint())) {
@@ -1207,28 +1205,30 @@ void ShelfLayoutManager::StartGestureDrag(
         shelf_bounds.y(), GetAppListBackgroundOpacityOnShelfOpacity());
     launcher_above_shelf_bottom_amount_ =
         shelf_bounds.bottom() - gesture_in_screen.location().y();
-  } else {
-    HomeLauncherGestureHandler* home_launcher_handler =
-        Shell::Get()->app_list_controller()->home_launcher_gesture_handler();
-    if (home_launcher_handler && IsVisible() &&
-        home_launcher_handler->OnPressEvent(
-            HomeLauncherGestureHandler::Mode::kSlideUpToShow,
-            gesture_in_screen.location())) {
-      gesture_drag_status_ = GESTURE_DRAG_APPLIST_IN_PROGRESS;
-      return;
-    }
-
-    // Disable the shelf dragging if the fullscreen app list is opened.
-    if (is_app_list_visible_ && !IsHomeLauncherEnabledInTabletMode())
-      return;
+    return true;
+  }
 
-    gesture_drag_status_ = GESTURE_DRAG_IN_PROGRESS;
-    gesture_drag_auto_hide_state_ = visibility_state() == SHELF_AUTO_HIDE
-                                        ? auto_hide_state()
-                                        : SHELF_AUTO_HIDE_SHOWN;
-    MaybeUpdateShelfBackground(AnimationChangeType::ANIMATE);
-    gesture_drag_amount_ = 0.f;
+  HomeLauncherGestureHandler* home_launcher_handler =
+      Shell::Get()->app_list_controller()->home_launcher_gesture_handler();
+  if (home_launcher_handler && IsVisible() &&
+      home_launcher_handler->OnPressEvent(
+          HomeLauncherGestureHandler::Mode::kSlideUpToShow,
+          gesture_in_screen.location())) {
+    gesture_drag_status_ = GESTURE_DRAG_APPLIST_IN_PROGRESS;
+    return true;
   }
+
+  // Disable the shelf dragging if the fullscreen app list is opened.
+  if (is_app_list_visible_ && !IsHomeLauncherEnabledInTabletMode())
+    return false;
+
+  gesture_drag_status_ = GESTURE_DRAG_IN_PROGRESS;
+  gesture_drag_auto_hide_state_ = visibility_state() == SHELF_AUTO_HIDE
+                                      ? auto_hide_state()
+                                      : SHELF_AUTO_HIDE_SHOWN;
+  MaybeUpdateShelfBackground(AnimationChangeType::ANIMATE);
+  gesture_drag_amount_ = 0.f;
+  return true;
 }
 
 void ShelfLayoutManager::UpdateGestureDrag(

ash/shelf/shelf_layout_manager.h

@@ -333,7 +333,7 @@ class ASH_EXPORT ShelfLayoutManager
   bool IsShelfAutoHideForFullscreenMaximized() const;
 
   // Gesture related functions:
-  void StartGestureDrag(const ui::GestureEvent& gesture_in_screen);
+  bool StartGestureDrag(const ui::GestureEvent& gesture_in_screen);
   void UpdateGestureDrag(const ui::GestureEvent& gesture_in_screen);
   void CompleteGestureDrag(const ui::GestureEvent& gesture_in_screen);
   void CompleteAppListDrag(const ui::GestureEvent& gesture_in_screen);

ash/shelf/shelf_layout_manager_unittest.cc

@@ -1587,6 +1587,50 @@ TEST_F(ShelfLayoutManagerTest, FlingUpOnShelfForFullscreenAppList) {
   GetAppListTestHelper()->CheckState(app_list::AppListViewState::PEEKING);
 }
 
+// Tests that duplicate swipe up from bottom bezel should not make app list
+// undraggable. (See https://crbug.com/896934)
+TEST_F(ShelfLayoutManagerTest, DuplicateDragUpFromBezel) {
+  GetAppListTestHelper()->CheckVisibility(false);
+  GetAppListTestHelper()->CheckState(app_list::AppListViewState::CLOSED);
+
+  // Start the drag from the bottom bezel to the area that snaps to fullscreen
+  // state.
+  gfx::Rect shelf_widget_bounds = GetShelfWidget()->GetWindowBoundsInScreen();
+  gfx::Point start =
+      gfx::Point(shelf_widget_bounds.x() + shelf_widget_bounds.width() / 2,
+                 shelf_widget_bounds.bottom() + 1);
+  gfx::Point end = gfx::Point(
+      start.x(), shelf_widget_bounds.bottom() -
+                     ShelfLayoutManager::kAppListDragSnapToPeekingThreshold -
+                     10);
+  ui::test::EventGenerator* generator = GetEventGenerator();
+  constexpr base::TimeDelta kTimeDelta = base::TimeDelta::FromMilliseconds(100);
+  constexpr int kNumScrollSteps = 4;
+  generator->GestureScrollSequence(start, end, kTimeDelta, kNumScrollSteps);
+  GetAppListTestHelper()->WaitUntilIdle();
+  GetAppListTestHelper()->CheckVisibility(true);
+  GetAppListTestHelper()->CheckState(
+      app_list::AppListViewState::FULLSCREEN_ALL_APPS);
+
+  // Start the same drag event from bezel.
+  generator->GestureScrollSequence(start, end, kTimeDelta, kNumScrollSteps);
+  GetAppListTestHelper()->WaitUntilIdle();
+  GetAppListTestHelper()->CheckVisibility(true);
+  GetAppListTestHelper()->CheckState(
+      app_list::AppListViewState::FULLSCREEN_ALL_APPS);
+
+  // Start the drag from top screen to the area that snaps to closed state. (The
+  // launcher is still draggable now.)
+  start.set_y(
+      display::Screen::GetScreen()->GetPrimaryDisplay().work_area().y());
+  end.set_y(shelf_widget_bounds.bottom() -
+            ShelfLayoutManager::kAppListDragSnapToClosedThreshold + 10);
+  generator->GestureScrollSequence(start, end, kTimeDelta, kNumScrollSteps);
+  GetAppListTestHelper()->WaitUntilIdle();
+  GetAppListTestHelper()->CheckVisibility(false);
+  GetAppListTestHelper()->CheckState(app_list::AppListViewState::CLOSED);
+}
+
 // Change the shelf alignment during dragging should dismiss the app list.
 TEST_F(ShelfLayoutManagerTest, ChangeShelfAlignmentDuringAppListDragging) {
   Shelf* shelf = GetPrimaryShelf();