overview gesture: clear wallpaper opacity set during window dragging.

Bug: 997885
Change-Id: Ib479e05d744d5e85c2319fb1873e1b94033320fe
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1875553Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Xiaoqian Dai <xdai@chromium.org>
Cr-Commit-Position: refs/heads/master@{#709179}

ash/home_screen/drag_window_from_shelf_controller.cc

@@ -419,10 +419,8 @@ void DragWindowFromShelfController::OnDragEnded(
         RootWindowController::ForWindow(window_->GetRootWindow())
             ->wallpaper_widget_controller()
             ->wallpaper_view();
-    if (wallpaper_view) {
-      wallpaper_view->RepaintBlurAndOpacity(kWallpaperClearBlurSigma,
-                                            kShieldOpacity);
-    }
+    if (wallpaper_view)
+      wallpaper_view->RepaintBlurAndOpacity(kWallpaperClearBlurSigma, 1.f);
   }
 
   WindowState::Get(window_)->DeleteDragDetails();