Wire up Android back button in SkyShell

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 99af729c85b0d4f153e9023ca9287700dd3e3077..2cbcccb49f6f60ad5afafb1b33e2418996b54723 100644
--- a/sky/shell/android/org/domokit/sky/shell/SkyActivity.java
+++ b/sky/shell/android/org/domokit/sky/shell/SkyActivity.java
@@ -48,6 +48,17 @@ public class SkyActivity extends Activity {
         super.onDestroy();
     }
 
+    @Override
+    public void onBackPressed() {
+        if (mView != null) {
+            mView.onBackPressed();
+            // TODO(abarth): We should have some way to trigger the default
+            // back behavior.
+            return;
+        }
+        super.onBackPressed();
+    }
+
     public void loadUrl(String url) {
         mView.loadUrl(url);
     }