Add a back stack to activities launched from notifications.

See
https://developer.android.com/guide/topics/ui/notifiers/notifications.html#NotificationResponse

briar-android/AndroidManifest.xml

@@ -58,7 +58,12 @@
 		<activity
 		    android:name=".android.contact.ContactListActivity"
 			android:logo="@drawable/logo"
-		    android:label="@string/contact_list_title" >
+		    android:label="@string/contact_list_title"
+		    android:parentActivityName=".android.HomeScreenActivity" >
+			<meta-data
+				android:name="android.support.PARENT_ACTIVITY"
+				android:value=".android.HomeScreenActivity"
+			/>
 		</activity>
 		<activity
 			android:name=".android.contact.ConversationActivity"
@@ -93,7 +98,12 @@
 		<activity
 			android:name=".android.groups.GroupListActivity"
 			android:logo="@drawable/logo"
-			android:label="@string/forums_title" >
+			android:label="@string/forums_title"
+		    android:parentActivityName=".android.HomeScreenActivity" >
+			<meta-data
+				android:name="android.support.PARENT_ACTIVITY"
+				android:value=".android.HomeScreenActivity"
+			/>
 		</activity>
 		<activity
 		    android:name=".android.groups.ManageGroupsActivity"

briar-android/src/org/briarproject/android/BriarService.java

@@ -38,6 +38,7 @@ import android.content.ServiceConnection;
 import android.os.Binder;
 import android.os.IBinder;
 import android.support.v4.app.NotificationCompat;
+import android.support.v4.app.TaskStackBuilder;
 
 public class BriarService extends RoboService implements EventListener {
 
@@ -192,7 +193,10 @@ public class BriarService extends RoboService implements EventListener {
 		b.setDefaults(DEFAULT_ALL);
 		Intent i = new Intent(this, ContactListActivity.class);
 		i.setFlags(FLAG_ACTIVITY_NEW_TASK | FLAG_ACTIVITY_SINGLE_TOP);
-		b.setContentIntent(PendingIntent.getActivity(this, 0, i, 0));
+		TaskStackBuilder tsb = TaskStackBuilder.create(this);
+		tsb.addParentStack(ContactListActivity.class);
+		tsb.addNextIntent(i);
+		b.setContentIntent(tsb.getPendingIntent(0, 0));
 		Object o = getSystemService(NOTIFICATION_SERVICE);
 		NotificationManager nm = (NotificationManager) o;
 		nm.notify(PRIVATE_MESSAGE_NOTIFICATION_ID, b.build());
@@ -207,7 +211,10 @@ public class BriarService extends RoboService implements EventListener {
 		b.setDefaults(DEFAULT_ALL);
 		Intent i = new Intent(this, GroupListActivity.class);
 		i.setFlags(FLAG_ACTIVITY_NEW_TASK | FLAG_ACTIVITY_SINGLE_TOP);
-		b.setContentIntent(PendingIntent.getActivity(this, 0, i, 0));
+		TaskStackBuilder tsb = TaskStackBuilder.create(this);
+		tsb.addParentStack(GroupListActivity.class);
+		tsb.addNextIntent(i);
+		b.setContentIntent(tsb.getPendingIntent(0, 0));
 		Object o = getSystemService(NOTIFICATION_SERVICE);
 		NotificationManager nm = (NotificationManager) o;
 		nm.notify(GROUP_POST_NOTIFICATION_ID, b.build());