@VisibleForTesting
    @NonNull
    public static CustomTabsSession createMockSessionForTesting(
            @NonNull ComponentName componentName) {
        return new CustomTabsSession(
                null, new CustomTabsSessionToken.MockCallback(), componentName, null);
    }
Provides browsers a way to generate a mock {@link CustomTabsSession} for testing
purposes.

@param componentName The component the session should be created for.
@return A mock session with no functionality.
customtabs/src/android/support/customtabs/CustomTabsSession.java