Show the auto-hide shelf if there is a single PIP window

This CL reverts https://crrev.com/c/1529500.

The reason why we hid the auto-hide shelf at the time is that we
didn't apply the collision detection logic to the PIP initial
bounds and the auto-hide shelf could overlap with PIP. Now that we
apply collision detection to the initial bounds, we can now revert
this CL.

Currently there are a few issues with PIP if the auto-hide shelf
gets hidden when there's a single PIP window.
- When you trigger PIP via minimize, the original window gets
  minimized first and the auto-hide shelf becomes shown, but soon
  after PIP shows up and the shelf becomes hidden again, which
  looks a bit weird.
- When PIP gets shown, the auto-hide shelf is still visible and
  then it gets hidden, but the PIP window doesn't move to the
  bottom as at this point the gravity is "to the right".

BUG=b:149889866
TEST=Manually confirmed the PIP interacts well with the auto-hide
TEST=shelf.

Change-Id: I643487b53b23931bdabd816a30c6337741d15fc4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2065256Reviewed-by: Eliot Courtney <edcourtney@chromium.org>
Reviewed-by: Stefan Kuhne <skuhne@chromium.org>
Commit-Queue: Kazuki Takise <takise@chromium.org>
Auto-Submit: Kazuki Takise <takise@chromium.org>
Cr-Commit-Position: refs/heads/master@{#743391}

ash/shelf/shelf_layout_manager.cc

@@ -846,10 +846,7 @@ bool ShelfLayoutManager::HasVisibleWindow() const {
       return true;
     }
   }
-  auto* pip_container = Shell::GetContainer(root, kShellWindowId_PipContainer);
-  // The PIP window is not activatable and is not in the MRU list, but count
-  // it as a visible window for shelf auto-hide purposes. See crbug.com/942991.
-  return !pip_container->children().empty();
+  return false;
 }
 
 void ShelfLayoutManager::CancelDragOnShelfIfInProgress() {

ash/shelf/shelf_layout_manager_unittest.cc

@@ -2374,8 +2374,8 @@ TEST_P(ShelfLayoutManagerTest, A11yAlertOnWorkspaceState) {
             client.last_a11y_alert());
 }
 
-// Verifies the auto-hide shelf is hidden if there is only a single PIP window.
-TEST_P(ShelfLayoutManagerTest, AutoHideShelfHiddenForSinglePipWindow) {
+// Verifies the auto-hide shelf is shown if there is only a single PIP window.
+TEST_P(ShelfLayoutManagerTest, AutoHideShelfShownForSinglePipWindow) {
   Shelf* shelf = GetPrimaryShelf();
   shelf->SetAutoHideBehavior(ShelfAutoHideBehavior::kAlways);
   EXPECT_EQ(SHELF_AUTO_HIDE, shelf->GetVisibilityState());
@@ -2394,7 +2394,7 @@ TEST_P(ShelfLayoutManagerTest, AutoHideShelfHiddenForSinglePipWindow) {
 
   // Expect the shelf to be hidden.
   EXPECT_EQ(SHELF_AUTO_HIDE, shelf->GetVisibilityState());
-  EXPECT_EQ(SHELF_AUTO_HIDE_HIDDEN, shelf->GetAutoHideState());
+  EXPECT_EQ(SHELF_AUTO_HIDE_SHOWN, shelf->GetAutoHideState());
 }
 
 // Verifies that shelf components are placed properly in right-to-left UI.