Expose SkPicture::willPlayBackBitmaps()

This returns true if (1) the picture has finished recording and
(2) this picture or any picture drawn into it refers to any bitmaps. 
It allows clients doing complicated manipulations of the picture to 
early-out when there are no bitmaps present. 

BUG=303281
R=reed@google.com



git-svn-id: http://skia.googlecode.com/svn/trunk@11935 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/src/core/SkPicturePlayback.h b/src/core/SkPicturePlayback.h
index 86c976c..6eb9ac3 100644
--- a/src/core/SkPicturePlayback.h
+++ b/src/core/SkPicturePlayback.h
@@ -73,6 +73,8 @@
 
     void dumpSize() const;
 
+    bool containsBitmaps() const;
+
 #ifdef SK_BUILD_FOR_ANDROID
     // Can be called in the middle of playback (the draw() call). WIll abort the
     // drawing and return from draw() after the "current" op code is done