back gesture: disable it by default.

The back gesture kSwipingFromLeftEdgeToGoBack feature is disabled by
default, and is only enabled on the devices that has hotseat feature
enabled (i.e., on Krane and on Dogfood devices).

Bug: 1030122, 1002733
Change-Id: Ie6fed45ff8df7113bc86923c23ac9e581da64937
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1947947Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Min Chen <minch@chromium.org>
Cr-Commit-Position: refs/heads/master@{#721067}

ash/public/cpp/ash_features.cc

@@ -102,7 +102,7 @@ const base::Feature kEnableBackgroundBlur{"EnableBackgroundBlur",
                                           base::FEATURE_ENABLED_BY_DEFAULT};
 
 const base::Feature kSwipingFromLeftEdgeToGoBack{
-    "SwipingFromLeftEdgeToGoBack", base::FEATURE_ENABLED_BY_DEFAULT};
+    "SwipingFromLeftEdgeToGoBack", base::FEATURE_DISABLED_BY_DEFAULT};
 
 const base::Feature kDragFromShelfToHomeOrOverview{
     "DragFromShelfToHomeOrOverview", base::FEATURE_DISABLED_BY_DEFAULT};
@@ -199,7 +199,11 @@ bool IsBackgroundBlurEnabled() {
 }
 
 bool IsSwipingFromLeftEdgeToGoBackEnabled() {
-  return base::FeatureList::IsEnabled(kSwipingFromLeftEdgeToGoBack);
+  // The kSwipingFromLeftEdgeToGoBack feature is only enabled on the devices
+  // that have hotseat enabled (i.e., on Krane and on Dogfood devices) in M80.
+  // See crbug.com/1030122 for details.
+  return base::FeatureList::IsEnabled(kSwipingFromLeftEdgeToGoBack) ||
+         chromeos::switches::ShouldShowShelfHotseat();
 }
 
 bool IsDragFromShelfToHomeOrOverviewEnabled() {