Don't layout behind the system bar if we can't make it transparent

R=abarth@google.com

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

@@ -37,9 +37,11 @@ public class SkyActivity extends Activity {
         if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
             getWindow().addFlags(WindowManager.LayoutParams.FLAG_DRAWS_SYSTEM_BAR_BACKGROUNDS);
             getWindow().setStatusBarColor(0x40000000);
+        }
         // TODO(abarth): We should get this value from the Android framework somehow.
         edgeDims.top = 25.0;
-        }
+        // TODO(abarth): Unclear if we want to use fullscreen if we don't have
+        // a transparent system bar.
         getWindow().getDecorView().setSystemUiVisibility(
                 View.SYSTEM_UI_FLAG_LAYOUT_STABLE
                 | View.SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN);