Add support for a new developer setting: overdraw debugging

Change-Id: I350ba4486577c3289f82c20938f7a35138778727
diff --git a/libs/hwui/Stencil.h b/libs/hwui/Stencil.h
index 67ccc78..2f8a66a 100644
--- a/libs/hwui/Stencil.h
+++ b/libs/hwui/Stencil.h
@@ -59,6 +59,16 @@
     void enableWrite();
 
     /**
+     * The test passes only when equal to the specified value.
+     */
+    void enableDebugTest(GLint value, bool greater = false);
+
+    /**
+     * Used for debugging. The stencil test always passes and increments.
+     */
+    void enableDebugWrite();
+
+    /**
      * Disables stencil test and write.
      */
     void disable();