Add machinery for dumping SkPictures to disk

sky/shell/gpu/picture_serializer.h

Index: sky/shell/gpu/picture_serializer.h
diff --git a/sky/viewer/compositor/picture_serializer.h b/sky/shell/gpu/picture_serializer.h
similarity index 66%
copy from sky/viewer/compositor/picture_serializer.h
copy to sky/shell/gpu/picture_serializer.h
index dfddb2b287eb15202287a8fdb4e6be96a5a1ac0d..f4300382ca55444abae75e8445910249e000c57c 100644
--- a/sky/viewer/compositor/picture_serializer.h
+++ b/sky/shell/gpu/picture_serializer.h
@@ -2,8 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#ifndef SKY_VIEWER_COMPOSITOR_PICTURE_SERIALIZER_H_
-#define SKY_VIEWER_COMPOSITOR_PICTURE_SERIALIZER_H_
+#ifndef SKY_SHELL_GPU_PICTURE_SERIALIZER_H_
+#define SKY_SHELL_GPU_PICTURE_SERIALIZER_H_
 
 #include "third_party/skia/include/core/SkPicture.h"
 
@@ -13,4 +13,4 @@ void SerializePicture(const char* file_name, SkPicture*);
 
 }  // namespace sky
 
-#endif  // SKY_VIEWER_COMPOSITOR_PICTURE_SERIALIZER_H_
+#endif  // SKY_SHELL_GPU_PICTURE_SERIALIZER_H_