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/tools/LazyDecodeBitmap.cpp b/tools/LazyDecodeBitmap.cpp
index 6c4160c..4459cf1 100644
--- a/tools/LazyDecodeBitmap.cpp
+++ b/tools/LazyDecodeBitmap.cpp
@@ -22,7 +22,7 @@
             "implementation.");
 
 //  Fits SkPicture::InstallPixelRefProc call signature.
-//  Used in SkPicturePlayback::CreateFromStream
+//  Used in SkPictureData::CreateFromStream
 bool sk_tools::LazyDecodeBitmap(const void* src,
                                 size_t length,
                                 SkBitmap* dst) {