Is there an official API for centered title on Toolbar like on popular Android apps, in the new material design?

TL;DR: No, there's currently no official way to center the title on a toolbar.

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I don't think there is an official way to do it, at least not yet. But I know that the Flutter framework supports it and it's pretty straight forward: you simply need to pass centerTitle: true to the appbar constructor, as described in this answer. And there's a good chance that the apps you've mentioned in your question were built with Flutter, since both are from Google.

I think the closest workaround to your expected layout is having the TextView on top of the Toolbar, as shown here:

<android.support.design.widget.AppBarLayout
    android:id="@+id/appbar_layout"
    android:layout_width="match_parent"
    android:layout_height="wrap_content">
    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

        <android.support.v7.widget.Toolbar
            android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:theme="@style/ThemeOverlay.AppCompat.ActionBar">
        </android.support.v7.widget.Toolbar>

        <TextView
            android:layout_centerInParent="true"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/app_name"/>

    </RelativeLayout>
</android.support.design.widget.AppBarLayout>

But it would be really nice if the official Android API could support this the same way flutter does. Maybe you'd like to send a feature request to the Material Components Android Issue Tracker?