overview: Remove default arguments to OverviewSession::AddItem

Bug: None
Change-Id: Ib901eeae6a357baaa9d25605aed71c58664b8dfc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2033889Reviewed-by: Sammie Quon <sammiequon@chromium.org>
Commit-Queue: Avery Musbach <amusbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#738297}

ash/wm/overview/overview_session.h

@@ -172,8 +172,8 @@ class ASH_EXPORT OverviewSession : public display::DisplayObserver,
   void AddItem(aura::Window* window,
                bool reposition,
                bool animate,
-               const base::flat_set<OverviewItem*>& ignored_items = {},
-               size_t index = 0);
+               const base::flat_set<OverviewItem*>& ignored_items,
+               size_t index);
 
   // Similar to the above function, but adds the window at the end of the grid.
   // This will use the spawn-item animation.

ash/wm/overview/overview_session_unittest.cc

@@ -1842,7 +1842,8 @@ TEST_P(OverviewSessionTest, NoWindowsIndicatorAddItem) {
   EXPECT_TRUE(overview_session()->no_windows_widget_for_testing());
 
   overview_session()->AddItem(window.get(), /*reposition=*/true,
-                              /*animate=*/false);
+                              /*animate=*/false, /*ignored_items=*/{},
+                              /*index=*/0u);
   EXPECT_FALSE(overview_session()->no_windows_widget_for_testing());
 }