[Android][A11y] Make the title field focusable for a11y

This CL makes the title field of web sign-in bottom sheet focusable
so that we can then send an a11y event from this field to announce the
title.

Bug: 1143259
Change-Id: I73f19a37dd5cf3a23454400149c4db2fc26db0f5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2577204Reviewed-by: Theresa  <twellington@chromium.org>
Commit-Queue: Alice Wang <aliceywang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#834279}

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

@@ -148,6 +148,7 @@ class AccountPickerBottomSheetView implements BottomSheetContent {
     void setDisplayedView(@ViewState int state) {
         mViewFlipper.setDisplayedChild(state);
         View titleView = mViewFlipper.getChildAt(state).findViewById(sTitleIds[state]);
+        titleView.setFocusable(true);
         titleView.sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_FOCUSED);
     }