Default to home screen scale transform during overview transitions

Home screen slide transitions (where home screen is translated when
getting shown/hidden) were used before new gestures were implemented.
We should eventually remove the transitions (when the drag window from
home or overview feature flag gets removed), but for now, starting to
default to home screen scaling animations.

BUG=None

Change-Id: Ia310a5599317565ab9774062546c85182a7dd5f5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2200080Reviewed-by: Xiaoqian Dai <xdai@chromium.org>
Commit-Queue: Toni Baržić <tbarzic@chromium.org>
Cr-Commit-Position: refs/heads/master@{#768576}

ash/home_screen/home_screen_controller.cc

@@ -341,10 +341,13 @@ void HomeScreenController::OnOverviewModeStarting() {
       IsHomeScreenVisible() &&
       (overview_enter_type == OverviewEnterExitType::kSlideInEnter ||
        overview_enter_type == OverviewEnterExitType::kFadeInEnter);
+  const bool use_scale_transition =
+      overview_enter_type == OverviewEnterExitType::kFadeInEnter ||
+      (features::IsDragFromShelfToHomeOrOverviewEnabled() &&
+       overview_enter_type != OverviewEnterExitType::kSlideInEnter);
   const HomeScreenPresenter::TransitionType transition =
-      overview_enter_type == OverviewEnterExitType::kFadeInEnter
-          ? HomeScreenPresenter::TransitionType::kScaleHomeOut
-          : HomeScreenPresenter::TransitionType::kSlideHomeOut;
+      use_scale_transition ? HomeScreenPresenter::TransitionType::kScaleHomeOut
+                           : HomeScreenPresenter::TransitionType::kSlideHomeOut;
 
   home_screen_presenter_.ScheduleOverviewModeAnimation(transition, animate);
 }
@@ -385,10 +388,13 @@ void HomeScreenController::OnOverviewModeEndingAnimationComplete(
   const bool animate =
       *overview_exit_type_ == OverviewEnterExitType::kSlideOutExit ||
       *overview_exit_type_ == OverviewEnterExitType::kFadeOutExit;
+  const bool use_scale_transition =
+      *overview_exit_type_ == OverviewEnterExitType::kFadeOutExit ||
+      (features::IsDragFromShelfToHomeOrOverviewEnabled() &&
+       *overview_exit_type_ != OverviewEnterExitType::kSlideOutExit);
   const HomeScreenPresenter::TransitionType transition =
-      *overview_exit_type_ == OverviewEnterExitType::kFadeOutExit
-          ? HomeScreenPresenter::TransitionType::kScaleHomeIn
-          : HomeScreenPresenter::TransitionType::kSlideHomeIn;
+      use_scale_transition ? HomeScreenPresenter::TransitionType::kScaleHomeIn
+                           : HomeScreenPresenter::TransitionType::kSlideHomeIn;
   overview_exit_type_ = base::nullopt;
 
   home_screen_presenter_.ScheduleOverviewModeAnimation(transition, animate);