Add incStrong and decStrong methods to android_native_{window,buffer}_t.

This change adds the methods necessary to use sp<> to handle refcounting
android_native_window_t and android_native_buffer_t.  The new methods forward
the refcounting operations to the corresponding android_native_base_t
functions.

Change-Id: I7de8e262728e439bc1efdf69374a2a9f6f432ced
diff --git a/include/ui/android_native_buffer.h b/include/ui/android_native_buffer.h
index 9c92af8..402843e 100644
--- a/include/ui/android_native_buffer.h
+++ b/include/ui/android_native_buffer.h
@@ -33,6 +33,15 @@
         common.version = sizeof(android_native_buffer_t);
         memset(common.reserved, 0, sizeof(common.reserved));
     }
+
+    // Implement the methods that sp<android_native_buffer_t> expects so that it
+    // can be used to automatically refcount android_native_buffer_t's.
+    void incStrong(const void* id) const {
+        common.incRef(const_cast<android_native_base_t*>(&common));
+    }
+    void decStrong(const void* id) const {
+        common.decRef(const_cast<android_native_base_t*>(&common));
+    }
 #endif
 
     struct android_native_base_t common;