Account for various launcher states when setting back button alpha

- Previously we only check for the flag which is always true in the
  normal launcher state, so if the animation starts, we could end up
  writing the back alpha value without accounting for window focus or
  any other states that launcher is in that affects back button
  visibility

Bug: 155129739
Test: Open -1 article and hit back
Change-Id: I42d27a192b23f394f8565a6893ce092603e31654

quickstep/src/com/android/launcher3/BaseQuickstepLauncher.java

@@ -252,13 +252,10 @@ public abstract class BaseQuickstepLauncher extends Launcher
         super.onActivityFlagsChanged(changeBits);
     }
 
-    /**
-     * Sets the back button visibility based on the current state/window focus.
-     */
-    private void onLauncherStateOrFocusChanged() {
+    public boolean shouldBackButtonBeHidden(LauncherState toState) {
         Mode mode = SysUINavigationMode.getMode(this);
         boolean shouldBackButtonBeHidden = mode.hasGestures
-                && getStateManager().getState().hasFlag(FLAG_HIDE_BACK_BUTTON)
+                && toState.hasFlag(FLAG_HIDE_BACK_BUTTON)
                 && hasWindowFocus()
                 && (getActivityFlags() & ACTIVITY_STATE_TRANSITION_ACTIVE) == 0;
         if (shouldBackButtonBeHidden) {
@@ -266,6 +263,14 @@ public abstract class BaseQuickstepLauncher extends Launcher
             shouldBackButtonBeHidden = AbstractFloatingView.getTopOpenViewWithType(this,
                     TYPE_ALL & ~TYPE_HIDE_BACK_BUTTON) == null;
         }
+        return shouldBackButtonBeHidden;
+    }
+
+    /**
+     * Sets the back button visibility based on the current state/window focus.
+     */
+    private void onLauncherStateOrFocusChanged() {
+        boolean shouldBackButtonBeHidden = shouldBackButtonBeHidden(getStateManager().getState());
         UiThreadHelper.setBackButtonAlphaAsync(this, SET_BACK_BUTTON_ALPHA,
                 shouldBackButtonBeHidden ? 0f : 1f, true /* animate */);
         if (getDragLayer() != null) {

quickstep/src/com/android/launcher3/statehandlers/BackButtonAlphaHandler.java

@@ -61,7 +61,7 @@ public class BackButtonAlphaHandler implements LauncherStateManager.StateHandler
 
         mBackAlpha.value = SystemUiProxy.INSTANCE.get(mLauncher).getLastBackButtonAlpha();
         animation.setFloat(mBackAlpha, VALUE,
-                toState.hasFlag(FLAG_HIDE_BACK_BUTTON) ? 0 : 1, LINEAR);
+                mLauncher.shouldBackButtonBeHidden(toState) ? 0 : 1, LINEAR);
     }
 
     private void updateBackAlpha() {