[Android][Test] Improve AccountPickerBottomSheetRenderTest

This CL improves AccountPickerBottomSheetRenderTest's account list
expanding action to reduce the flakiness.

Bug: 1127676
Change-Id: Id0849d4c388151b2752a3678a722cac05eb7e9cd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2407255Reviewed-by: Tanmoy Mollik <triploblastic@chromium.org>
Commit-Queue: Alice Wang <aliceywang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#806691}

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

@@ -142,7 +142,7 @@ public class AccountPickerBottomSheetRenderTest {
         mAccountManagerTestRule.addAccount(PROFILE_DATA1);
         mAccountManagerTestRule.addAccount(PROFILE_DATA2);
         buildAndShowCollapsedBottomSheet();
-        onView(withText(PROFILE_DATA1.getFullName())).perform(click());
+        expandBottomSheet();
         mRenderTestRule.render(mCoordinator.getBottomSheetViewForTesting(), "expanded_sheet");
     }
 
@@ -155,7 +155,7 @@ public class AccountPickerBottomSheetRenderTest {
         mAccountManagerTestRule.addAccount(PROFILE_DATA1);
         mAccountManagerTestRule.addAccount(PROFILE_DATA2);
         buildAndShowCollapsedBottomSheet();
-        onView(withText(PROFILE_DATA1.getFullName())).perform(click());
+        expandBottomSheet();
         onView(withText(R.string.signin_incognito_mode_primary)).perform(click());
         onView(isRoot()).perform(pressBack());
         mRenderTestRule.render(mCoordinator.getBottomSheetViewForTesting(), "expanded_sheet");
@@ -271,6 +271,13 @@ public class AccountPickerBottomSheetRenderTest {
                 mCoordinator.getBottomSheetViewForTesting(), "signin_in_progress_sheet");
     }
 
+    private void expandBottomSheet() {
+        View view = mCoordinator.getBottomSheetViewForTesting();
+        TestThreadUtils.runOnUiThreadBlocking(
+                () -> { view.findViewById(R.id.account_picker_selected_account).performClick(); });
+        CriteriaHelper.pollUiThread(view.findViewById(R.id.account_picker_account_list)::isShown);
+    }
+
     private void buildAndShowCollapsedBottomSheet() {
         TestThreadUtils.runOnUiThreadBlocking(() -> {
             mCoordinator = new AccountPickerBottomSheetCoordinator(mActivityTestRule.getActivity(),