[Expressive design] Add toolbar buttons initialization API

Bug: 429130893
Test: visual
Flag: EXEMPT activity small refactor
Change-Id: I95bdd7d965f8b0bd01f3ba5e75f660da6e56d146
Signed-off-by: Stefan Maftei <smaftei@google.com>
diff --git a/packages/SettingsLib/CollapsingToolbarBaseActivity/src/com/android/settingslib/collapsingtoolbar/CollapsingToolbarDelegate.java b/packages/SettingsLib/CollapsingToolbarBaseActivity/src/com/android/settingslib/collapsingtoolbar/CollapsingToolbarDelegate.java
index c07bbf8..9309d5f 100644
--- a/packages/SettingsLib/CollapsingToolbarBaseActivity/src/com/android/settingslib/collapsingtoolbar/CollapsingToolbarDelegate.java
+++ b/packages/SettingsLib/CollapsingToolbarBaseActivity/src/com/android/settingslib/collapsingtoolbar/CollapsingToolbarDelegate.java
@@ -179,9 +179,9 @@
             }
         }
 
-        mPrimaryButton = view.findViewById(R.id.primary_button);
-        mSecondaryButton = view.findViewById(R.id.secondary_button);
-        mActionButton = view.findViewById(R.id.action_button);
+        initToolbarPrimaryButton(view.findViewById(R.id.primary_button));
+        initToolbarSecondaryButton(view.findViewById(R.id.secondary_button));
+        initToolbarActionButton(view.findViewById(R.id.action_button));
 
         initFloatingToolbar(context, view.findViewById(R.id.floating_toolbar));
         return view;
@@ -209,6 +209,21 @@
         autoSetCollapsingToolbarLayoutScrolling(appBarLayout);
     }
 
+    /** Initialize toolbar's primary button. */
+    public void initToolbarPrimaryButton(MaterialButton primaryButton) {
+        mPrimaryButton = primaryButton;
+    }
+
+    /** Initialize toolbar's secondary button. */
+    public void initToolbarSecondaryButton(MaterialButton secondaryButton) {
+        mSecondaryButton = secondaryButton;
+    }
+
+    /** Initialize toolbar's action button. */
+    public void initToolbarActionButton(MaterialButton actionButton) {
+        mActionButton = actionButton;
+    }
+
     /**
      * Initialize the floating toolbar.
      * @param context