Back button should be able to close apps

sky/shell/android/org/domokit/sky/shell/SkyActivity.java

Index: sky/shell/android/org/domokit/sky/shell/SkyActivity.java
diff --git a/sky/shell/android/org/domokit/sky/shell/SkyActivity.java b/sky/shell/android/org/domokit/sky/shell/SkyActivity.java
index ef1fa1cc40709c1f490aa66e987b39717099831a..1e13dd36f5ab6a3bff95e12e952463f6806804cd 100644
--- a/sky/shell/android/org/domokit/sky/shell/SkyActivity.java
+++ b/sky/shell/android/org/domokit/sky/shell/SkyActivity.java
@@ -12,6 +12,8 @@ import android.view.WindowManager;
 
 import org.chromium.base.PathUtils;
 
+import org.domokit.intents.ActivityManagerImpl;
+
 import java.io.File;
 
 /**
@@ -42,6 +44,7 @@ public class SkyActivity extends Activity {
 
         SkyMain.ensureInitialized(getApplicationContext());
         mView = new PlatformViewAndroid(this, edgeDims);
+        ActivityManagerImpl.setCurrentActivity(this);
         setContentView(mView);
         mTracingController = new TracingController(this);