Remove unnecessary return and add bitmap generation ID tracking.

Change-Id: Icf5e0635e789f5ea53268c22fad51cf733b5b1a6
diff --git a/libs/hwui/Texture.h b/libs/hwui/Texture.h
index b3b17ca..6802c59 100644
--- a/libs/hwui/Texture.h
+++ b/libs/hwui/Texture.h
@@ -31,6 +31,10 @@
      */
     GLuint id;
     /**
+     * Generation of the backing bitmap,
+     */
+    uint32_t generation;
+    /**
      * Indicates whether the texture requires blending.
      */
     bool blend;