Add ifdef to prevent header being added multiple times.

Change-Id: I92bb0667bea98e43fca20dceb4fff20e446c03cf
diff --git a/core/jni/android/graphics/NinePatchPeeker.h b/core/jni/android/graphics/NinePatchPeeker.h
index 1f37b8b..8567e23 100644
--- a/core/jni/android/graphics/NinePatchPeeker.h
+++ b/core/jni/android/graphics/NinePatchPeeker.h
@@ -14,6 +14,9 @@
  * limitations under the License.
  */
 
+#ifndef NinePatchPeeker_h
+#define NinePatchPeeker_h
+
 #include "SkImageDecoder.h"
 #include <utils/ResourceTypes.h>
 
@@ -40,3 +43,4 @@
     virtual bool peek(const char tag[], const void* data, size_t length);
 };
 
+#endif // NinePatchPeeker_h