Add context support to backdropper filter.

Part of b/7028438

Change-Id: Idcae38b452abc847c7b869a5568d1c5d831411b7

Author: midodd

media/mca/effect/java/android/media/effect/effects/BackDropperEffect.java

@@ -91,6 +91,9 @@ public void setParameter(String parameterKey, Object value) {
         if (parameterKey.equals("source")) {
             Filter background = mGraph.getFilter("background");
             background.setInputValue("sourceUrl", value);
+        } else if (parameterKey.equals("context")) {
+            Filter background = mGraph.getFilter("background");
+            background.setInputValue("context", value);
         }
     }