Rename SkPicturePlayback to SkPictureData

This is in preparation for splitting the playback portion of the new SkPictureData class into a new SkPicturePlayback class.

R=reed@google.com, mtklein@google.com

Author: robertphillips@google.com

Review URL: https://codereview.chromium.org/362773002
diff --git a/src/core/SkPictureRecord.h b/src/core/SkPictureRecord.h
index 417dde6..0fdfaa7 100644
--- a/src/core/SkPictureRecord.h
+++ b/src/core/SkPictureRecord.h
@@ -15,7 +15,7 @@
 #endif
 #include "SkPathHeap.h"
 #include "SkPicture.h"
-#include "SkPicturePlayback.h"
+#include "SkPictureData.h"
 #include "SkPictureFlat.h"
 #include "SkTemplates.h"
 #include "SkWriter32.h"
@@ -325,7 +325,7 @@
     bool     fOptsEnabled;
     int      fInitialSaveCount;
 
-    friend class SkPicturePlayback;
+    friend class SkPictureData;
     friend class SkPictureTester; // for unit testing
 
 #ifdef SK_COLLAPSE_MATRIX_CLIP_STATE