[Signin][Android] Add empty onDismiss method to AccountPickerDelegate

This CL adds an empty method onDismiss to AccountPickerDelegate so we
can release resources in this method later when working with
WebSigninBridge.

Bug: 1093741
Change-Id: Ibcea89c360431e102115faa3e7b34eb435253252
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2339514Reviewed-by: Tanmoy Mollik <triploblastic@chromium.org>
Commit-Queue: Alice Wang <aliceywang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#795363}

chrome/android/java/src/org/chromium/chrome/browser/signin/account_picker/AccountPickerBottomSheetMediator.java

@@ -84,6 +84,7 @@ class AccountPickerBottomSheetMediator implements AccountPickerCoordinator.Liste
     }
 
     void destroy() {
+        mAccountPickerDelegate.onDismiss();
         mProfileDataCache.removeObserver(mProfileDataSourceObserver);
         mAccountManagerFacade.removeObserver(mAccountsChangeObserver);
     }

chrome/android/java/src/org/chromium/chrome/browser/signin/account_picker/AccountPickerDelegate.java

@@ -47,6 +47,14 @@ public class AccountPickerDelegate {
         mSigninManager = IdentityServicesProvider.get().getSigninManager(
                 Profile.getLastUsedRegularProfile());
     }
+
+    /**
+     * Releases resources used by this class.
+     */
+    public void onDismiss() {
+        // TODO(https://crbug.com/1093741): Destroys WebSigninBridge in the delegate
+    }
+
     /**
      * Signs the user into the account of the given accountName.
      */

chrome/android/javatests/src/org/chromium/chrome/browser/signin/AccountPickerBottomSheetTest.java

@@ -195,6 +195,7 @@ public class AccountPickerBottomSheetTest {
         Assert.assertEquals(2, mFakeProfileDataSource.getNumberOfObservers());
         onView(isRoot()).perform(pressBack());
         Assert.assertFalse(controller.isSheetOpen());
+        verify(mAccountPickerDelegateMock).onDismiss();
         Assert.assertEquals(0, mFakeProfileDataSource.getNumberOfObservers());
     }
 
@@ -207,6 +208,7 @@ public class AccountPickerBottomSheetTest {
         Assert.assertEquals(2, mFakeProfileDataSource.getNumberOfObservers());
         onView(isRoot()).perform(pressBack());
         Assert.assertFalse(controller.isSheetOpen());
+        verify(mAccountPickerDelegateMock).onDismiss();
         Assert.assertEquals(0, mFakeProfileDataSource.getNumberOfObservers());
     }