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/gyp/core.gypi b/gyp/core.gypi
index d3e195a..0775e52 100644
--- a/gyp/core.gypi
+++ b/gyp/core.gypi
@@ -129,10 +129,10 @@
         '<(skia_src_path)/core/SkPathMeasure.cpp',
         '<(skia_src_path)/core/SkPathRef.cpp',
         '<(skia_src_path)/core/SkPicture.cpp',
+        '<(skia_src_path)/core/SkPictureData.cpp',
+        '<(skia_src_path)/core/SkPictureData.h',
         '<(skia_src_path)/core/SkPictureFlat.cpp',
         '<(skia_src_path)/core/SkPictureFlat.h',
-        '<(skia_src_path)/core/SkPicturePlayback.cpp',
-        '<(skia_src_path)/core/SkPicturePlayback.h',
         '<(skia_src_path)/core/SkPictureRecord.cpp',
         '<(skia_src_path)/core/SkPictureRecord.h',
         '<(skia_src_path)/core/SkPictureRecorder.cpp',