Unit test improvements to fully validate the SkImage contract

src/image/SkImage_Picture.cpp

Index: src/image/SkImage_Picture.cpp
===================================================================
--- src/image/SkImage_Picture.cpp	(revision 8614)
+++ src/image/SkImage_Picture.cpp	(working copy)
@@ -16,6 +16,8 @@
 
     virtual void onDraw(SkCanvas*, SkScalar, SkScalar, const SkPaint*) SK_OVERRIDE;
 
+    SkPicture* getPicture() { return fPicture; }
+
 private:
     SkPicture*  fPicture;
 
@@ -52,3 +54,7 @@
 
     return SkNEW_ARGS(SkImage_Picture, (playback));
 }
+
+SkPicture* SkPictureImageGetPicture(SkImage* pictureImage) {
+    return static_cast<SkImage_Picture*>(pictureImage)->getPicture();
+}