overview: Remove minimum scroll limit for new layout.

remove a performance related change which throttles some update
events, UX did not like the look. Also stop drags if display changes, to
avoid some weird looking states.

Test: manual
Bug: 1011449
Change-Id: I4bcb75e0b57975a511f75a65871bcff3b1e24719
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1856923Reviewed-by: Xiaoqian Dai <xdai@chromium.org>
Commit-Queue: Sammie Quon <sammiequon@chromium.org>
Cr-Commit-Position: refs/heads/master@{#705382}

ash/wm/overview/overview_grid.cc

@@ -77,9 +77,6 @@ constexpr int kTabletLayoutRow = 2;
 
 constexpr int kMinimumItemsForNewLayout = 6;
 
-// The minimum distance that is needed to process a scroll event.
-constexpr float kMinimumScrollDistanceDp = 5.f;
-
 // Wait a while before unpausing the occlusion tracker after a scroll has
 // completed as the user may start another scroll.
 constexpr base::TimeDelta kOcclusionUnpauseDurationForScroll =
@@ -1448,7 +1445,6 @@ void OverviewGrid::StartScroll() {
   // |scroll_offset_| is added to adjust for that.
   rightmost_window_right -= scroll_offset_;
   scroll_offset_min_ = total_bounds.right() - rightmost_window_right;
-  scroll_current_delta_ = 0.f;
 
   presentation_time_recorder_ = CreatePresentationTimeHistogramRecorder(
       const_cast<ui::Compositor*>(root_window()->layer()->GetCompositor()),
@@ -1456,9 +1452,8 @@ void OverviewGrid::StartScroll() {
 }
 
 bool OverviewGrid::UpdateScrollOffset(float delta) {
-  scroll_current_delta_ += delta;
   float new_scroll_offset = scroll_offset_;
-  new_scroll_offset += scroll_current_delta_;
+  new_scroll_offset += delta;
   new_scroll_offset =
       base::ClampToRange(new_scroll_offset, scroll_offset_min_, 0.f);
 
@@ -1469,13 +1464,6 @@ bool OverviewGrid::UpdateScrollOffset(float delta) {
   if (new_scroll_offset == scroll_offset_)
     return in_range;
 
-  // Do not process scrolls that haven't moved much, unless we are at the
-  // edges.
-  if (std::abs(scroll_offset_ - new_scroll_offset) < kMinimumScrollDistanceDp &&
-      in_range) {
-    return true;
-  }
-
   // Update the bounds of the items which are currently visible on screen.
   DCHECK_EQ(items_scrolling_bounds_.size(), window_list_.size());
   for (size_t i = 0; i < items_scrolling_bounds_.size(); ++i) {
@@ -1488,7 +1476,6 @@ bool OverviewGrid::UpdateScrollOffset(float delta) {
     }
   }
 
-  scroll_current_delta_ = 0.f;
   scroll_offset_ = new_scroll_offset;
 
   DCHECK(presentation_time_recorder_);

ash/wm/overview/overview_grid.h

@@ -452,10 +452,6 @@ class ASH_EXPORT OverviewGrid : public SplitViewObserver,
   // are visible in tablet overview mode.
   float scroll_offset_min_ = 0;
 
-  // Sum of the deltas passed by |UpdateScrollOffset|, this is so we can ignore
-  // deltas that are too small for performance reasons.
-  float scroll_current_delta_ = 0.f;
-
   // Cached values of the item bounds so that they do not have to be calculated
   // on each scroll update.
   std::vector<gfx::RectF> items_scrolling_bounds_;

ash/wm/overview/overview_session.cc

@@ -746,6 +746,8 @@ void OverviewSession::OnDisplayRemoved(const display::Display& display) {
 
 void OverviewSession::OnDisplayMetricsChanged(const display::Display& display,
                                               uint32_t metrics) {
+  if (window_drag_controller_)
+    ResetDraggedWindowGesture();
   GetGridWithRootWindow(Shell::GetRootWindowForDisplayId(display.id()))
       ->OnDisplayMetricsChanged();