Boton Toggle para abrir drawer

[Merche300]

Estoy intentando meter un tab a mi app, creada desde cero con la plantilla de navigation drawer con android studio, pero no me funciona el boton toggle en, Tab.class, para abrir el drawer, como lo consigo?

Tab.class

public class Tab extends AppCompatActivity {

private SectionsPagerAdapter mSectionsPagerAdapter;


private ViewPager mViewPager;

override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_tab);

Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);

mSectionsPagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager());


mViewPager = (ViewPager) findViewById(R.id.container);
mViewPager.setAdapter(mSectionsPagerAdapter);

TabLayout tabLayout = (TabLayout) findViewById(R.id.tabs);
tabLayout.setupWithViewPager(mViewPager);
Toolbar tb = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(tb);
ActionBar ab = getSupportActionBar();
ab.setHomeAsUpIndicator(drawer_toggle);
ab.setDisplayHomeAsUpEnabled(true);
}

override
public boolean onCreateOptionsMenu(Menu menu) {

getMenuInflater().inflate(R.menu.main, menu);
return true;
}

override
public boolean onOptionsItemSelected(MenuItem item) {

int id = item.getItemId();

if (id == R.id.action_settings) {
return true;
}

return super.onOptionsItemSelected(item);
}

public static class PlaceholderFragment extends Fragment {

private static final String ARG_SECTION_NUMBER = "section_number";

public PlaceholderFragment() {
}

public static PlaceholderFragment newInstance(int sectionNumber) {
PlaceholderFragment fragment = new PlaceholderFragment();
Bundle args = new Bundle();
args.putInt(ARG_SECTION_NUMBER, sectionNumber);
fragment.setArguments(args);
return fragment;
}

override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_tab, container, false);
TextView textView = (TextView) rootView.findViewById(R.id.section_label);
textView.setText(getString(R.string.section_format , getArguments().getInt(ARG_SECTION_NUMBER)));
return rootView;
}
}

public class SectionsPagerAdapter extends FragmentPagerAdapter {

public SectionsPagerAdapter(FragmentManager fm) {
super(fm);
}

override
public Fragment getItem(int position) {
return PlaceholderFragment.newInstance(position + 1);
}

override
public int getCount() {
return 3;
}

override
public CharSequence getPageTitle(int position) {
switch (position) {
case 0:
return "SECTION 1";
case 1:
return "SECTION 2";
case 2:
return "SECTION 3";
}
return null;
}
}

activity_tab.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.AppBarLayout
android:id="@+id/appbar"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:paddingTop="@dimen/appbar_padding_top"
android:theme="@style/AppTheme.AppBarOverlay">

<android.support.v7.widget.Toolbar
android:id="@+id/toolbar"
android:layout_width="match_parent"
android:layout_height="?attr/actionBarSize"
android:background="?attr/colorPrimary"
app:layout_scrollFlags="scroll|enterAlways"
app:popupTheme="@style/AppTheme.PopupOverlay">

</android.support.v7.widget.Toolbar>

<android.support.design.widget.TabLayout
android:id="@+id/tabs"
android:layout_width="match_parent"
android:layout_height="wrap_content" />

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

<android.support.v4.view.ViewPager
android:id="@+id/container"
android:layout_width="match_parent"
android:layout_height="match_parent"
app:layout_behavior="@string/appbar_scrolling_view_behavior" />

<android.support.design.widget.FloatingActionButton
android:id="@+id/fab"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="end|bottom"
android:layout_margin="@dimen/fab_margin"
app:srcCompat="@android:drawable/ic_dialog_email" />

Gracias