Revert "tablet: Fix double shelf when entering guest mode."

This reverts commit b1af29a5.

Reason for revert: Crashes ash_unittests on linux-chromeos-dbg

First failure: https://ci.chromium.org/p/chromium/builders/ci/linux-chromeos-dbg/16451

Original change's description:
> tablet: Fix double shelf when entering guest mode.
> 
> The issue was the window was created on startup, then OnGetSwitchStates
> triggers TabletMode to start and create the screenshot since it detects
> a window animating. But the window doesn't destroy the screenshot because
> a |fps_counter_| is not detected on animation end because it is created
> in on animation schedules which happened before entering tablet mode.
> 
> This CL aims to prevent this and similar bugs by not taking the screenshot
> if a window is already animating, so the only observed animation is the
> one triggered by entering tablet mode. This may have missed data or
> performance in some cases, but will prevent similar bugs.
> 
> Test: ash_unittests TabletModeControllerScreenshotTest.EnterTabletModeWhileAnimating
> Bug: 1035356
> Change-Id: I601d08ef50f214dbd262e5eea6baed40e5596270
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1999241
> Commit-Queue: Sammie Quon <sammiequon@chromium.org>
> Reviewed-by: Xiaoqian Dai <xdai@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#732159}

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

Change-Id: I738e9d46e2a9c7aa00305ba5ecf3c203ac872ecb
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 1035356
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2004177Reviewed-by: Meredith Lane <meredithl@chromium.org>
Commit-Queue: Meredith Lane <meredithl@chromium.org>
Cr-Commit-Position: refs/heads/master@{#732266}

ash/wm/tablet_mode/tablet_mode_controller.cc

@@ -619,11 +619,6 @@ void TabletModeController::OnLayerAnimationAborted(
 
 void TabletModeController::OnLayerAnimationEnded(
     ui::LayerAnimationSequence* sequence) {
-  // This may be called before |OnLayerAnimationScheduled()| if tablet is
-  // entered/exited while an animation is in progress, so we won't get
-  // stats/screenshot in those cases.
-  // TODO(sammiequon): We may want to remove the |fps_counter_| check and
-  // simplify things since those are edge cases.
   if (!fps_counter_ || !IsTransformAnimationSequence(sequence))
     return;
 
@@ -681,28 +676,21 @@ void TabletModeController::SetTabletModeEnabledInternal(bool should_enable) {
     state_ = State::kEnteringTabletMode;
 
     // Take a screenshot if there is a top window that will get animated.
+    // Since with ash::features::kDragToSnapInClamshellMode enabled, we'll keep
+    // overview active after clamshell <-> tablet mode transition if it was
+    // active before transition, do not take screenshot if overview is active
+    // in this case.
     // TODO(sammiequon): Handle the case where the top window is not on the
     // primary display.
     aura::Window* top_window = TabletModeWindowManager::GetTopWindow();
     const bool top_window_on_primary_display =
         top_window &&
         top_window->GetRootWindow() == Shell::GetPrimaryRootWindow();
-    // If the top window was already animating (eg. tablet mode event received
-    // while create window animation still running), skip taking the screenshot.
-    // It will take a performance hit but will remove cases where the screenshot
-    // might not get deleted because of the extra animation observer methods
-    // getting fired.
-    const bool top_window_animating =
-        top_window && top_window->layer()->GetAnimator()->is_animating();
-    // Since with ash::features::kDragToSnapInClamshellMode enabled, we'll keep
-    // overview active after clamshell <-> tablet mode transition if it was
-    // active before transition, do not take screenshot if overview is active
-    // in this case.
     const bool overview_remain_active =
         IsClamshellSplitViewModeEnabled() &&
         Shell::Get()->overview_controller()->InOverviewSession();
     if (use_screenshot_for_test && top_window_on_primary_display &&
-        !top_window_animating && !overview_remain_active) {
+        !overview_remain_active) {
       TakeScreenshot(top_window);
     } else {
       FinishInitTabletMode();

ash/wm/tablet_mode/tablet_mode_controller_unittest.cc

@@ -1685,30 +1685,12 @@ TEST_P(TabletModeControllerScreenshotTest, DISABLED_FromOverviewNoScreenshot) {
   EXPECT_FALSE(IsScreenshotShown());
 }
 
-// Regression test for screenshot staying visible when entering tablet mode when
-// a window creation animation is still underway. See https://crbug.com/1035356.
-TEST_P(TabletModeControllerScreenshotTest, EnterTabletModeWhileAnimating) {
-  auto window = CreateTestWindow(gfx::Rect(200, 200));
-  ASSERT_TRUE(window->layer()->GetAnimator()->is_animating());
-
-  // Enter tablet mode.
-  TabletMode::Waiter waiter(/*enable=*/true);
-  SetTabletMode(true);
-  EXPECT_FALSE(IsScreenshotShown());
-
-  waiter.Wait();
-  EXPECT_FALSE(IsScreenshotShown());
-}
-
 // Tests that the screenshot is visible when a window animation happens when
 // entering tablet mode.
 TEST_P(TabletModeControllerScreenshotTest, ScreenshotVisibility) {
   auto window = CreateTestWindow(gfx::Rect(200, 200));
   auto window2 = CreateTestWindow(gfx::Rect(300, 200));
-
-  window->layer()->GetAnimator()->StopAnimating();
   ui::Layer* layer = window2->layer();
-  layer->GetAnimator()->StopAnimating();
   ASSERT_FALSE(IsScreenshotShown());
 
   TabletMode::Waiter waiter(/*enable=*/true);
@@ -1731,7 +1713,6 @@ TEST_P(TabletModeControllerScreenshotTest, ScreenshotVisibility) {
 TEST_P(TabletModeControllerScreenshotTest, NoCrashWhenExitingWithoutWaiting) {
   // One non-maximized window is needed for screenshot to be taken.
   auto window = CreateTestWindow(gfx::Rect(200, 200));
-  window->layer()->GetAnimator()->StopAnimating();
 
   SetTabletMode(true);
   SetTabletMode(false);