SkPictureImageGenerator.h include guard

Change-Id: I6d9894ce3db427985c000b431fb79388c211b70c
Reviewed-on: https://skia-review.googlesource.com/8455
Reviewed-by: Hal Canary <halcanary@google.com>
Commit-Queue: Hal Canary <halcanary@google.com>

src/core/SkPictureImageGenerator.h

@@ -4,6 +4,8 @@
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
+#ifndef SkPictureImageGenerator_DEFINED
+#define SkPictureImageGenerator_DEFINED
 
 #include "SkImageGenerator.h"
 #include "SkTLazy.h"
@@ -33,3 +35,4 @@ private:
 
     typedef SkImageGenerator INHERITED;
 };
+#endif  // SkPictureImageGenerator_DEFINED