[CrOS PerfTest] Window Dragging in Overview

New test does following scenarios.
* Just drag
* Drag to close
* Drag to snap

This also fixes the bug in OverviewItem. It was using the current
opacity which can be non 1 during show animation. It should use
target opacity instead.

Bug: 948324
Change-Id: I545cd7402c04704e640e2bd70fcebc3fbc69283b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1563151
Commit-Queue: Mitsuru Oshima <oshima@chromium.org>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#650370}

ash/wm/overview/overview_item.cc

@@ -590,7 +590,7 @@ void OverviewItem::SetOpacity(float opacity) {
 }
 
 float OverviewItem::GetOpacity() {
-  return item_widget_->GetNativeWindow()->layer()->opacity();
+  return item_widget_->GetNativeWindow()->layer()->GetTargetOpacity();
 }
 
 OverviewAnimationType OverviewItem::GetExitOverviewAnimationType() {

chrome/test/BUILD.gn

@@ -5227,6 +5227,7 @@ if (!is_android) {
         "../browser/ui/ash/drag_to_overview_interactive_uitest.cc",
         "../browser/ui/ash/launcher_animations_interactive_uitest.cc",
         "../browser/ui/ash/overview_animations_interactive_uitest.cc",
+        "../browser/ui/ash/overview_window_drag_interactive_uitest.cc",
         "../browser/ui/ash/split_view_interactive_uitest.cc",
       ]
     } else {  # ! is_chromeos