Implement RS GC worker thread.

Bug 8579360

Change-Id: I98a5509b68e592bcbb4958f2ca72c236a22910b5
diff --git a/graphics/java/android/renderscript/ScriptC.java b/graphics/java/android/renderscript/ScriptC.java
index 108b230..9221c7a 100644
--- a/graphics/java/android/renderscript/ScriptC.java
+++ b/graphics/java/android/renderscript/ScriptC.java
@@ -60,6 +60,8 @@
             throw new RSRuntimeException("Loading of ScriptC script failed.");
         }
         setID(id);
+        mGCSize = 2 * 1024 * 1024;
+        rs.addAllocSizeForGC(mGCSize);
     }