clean up SkPicture include

Get SkPicture.h ready for documenting.

- remove private methods
- move private forward declarations
- name parameters

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

Bug: skia:6898
Change-Id: I28829111203d8ae2a4661cf02c99023403aa0df0
Reviewed-on: https://skia-review.googlesource.com/134120
Reviewed-by: Brian Salomon <bsalomon@google.com>
Reviewed-by: Cary Clark <caryclark@skia.org>
Commit-Queue: Cary Clark <caryclark@google.com>
diff --git a/src/effects/SkPictureImageFilter.cpp b/src/effects/SkPictureImageFilter.cpp
index df11e6c..b9c298d 100644
--- a/src/effects/SkPictureImageFilter.cpp
+++ b/src/effects/SkPictureImageFilter.cpp
@@ -12,6 +12,7 @@
 #include "SkColorSpaceXformer.h"
 #include "SkFlattenablePriv.h"
 #include "SkImageSource.h"
+#include "SkPicturePriv.h"
 #include "SkReadBuffer.h"
 #include "SkSpecialImage.h"
 #include "SkSpecialSurface.h"
@@ -58,7 +59,7 @@
     SkRect cropRect;
 
     if (buffer.readBool()) {
-        picture = SkPicture::MakeFromBuffer(buffer);
+        picture = SkPicturePriv::MakeFromBuffer(buffer);
     }
     buffer.readRect(&cropRect);
 
@@ -77,7 +78,7 @@
     bool hasPicture = (fPicture != nullptr);
     buffer.writeBool(hasPicture);
     if (hasPicture) {
-        fPicture->flatten(buffer);
+        SkPicturePriv::Flatten(fPicture, buffer);
     }
     buffer.writeRect(fCropRect);
 }