Mark SkDrawPictureCallback with SK_API, so that it can be derived from by SK_API classes

R=reed@google.com

Author: vmpstr@chromium.org

Review URL: https://chromiumcodereview.appspot.com/15745015

git-svn-id: http://skia.googlecode.com/svn/trunk@9249 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/include/core/SkPicture.h b/include/core/SkPicture.h
index 156d098..82afef0 100644
--- a/include/core/SkPicture.h
+++ b/include/core/SkPicture.h
@@ -277,7 +277,7 @@
  *  calls to save(), restore will automatically be called to return the state
  *  to the same level it was before the drawPicture call was made.
  */
-class SkDrawPictureCallback {
+class SK_API SkDrawPictureCallback {
 public:
     SkDrawPictureCallback() {}
     virtual ~SkDrawPictureCallback() {}