First pass at pre-rendering saveLayers for GPU

src/gpu/GrPictureUtils.cpp

Index: src/gpu/GrPictureUtils.cpp
===================================================================
--- src/gpu/GrPictureUtils.cpp	(revision 14572)
+++ src/gpu/GrPictureUtils.cpp	(working copy)
@@ -9,6 +9,7 @@
 #include "SkDevice.h"
 #include "SkDraw.h"
 #include "SkPaintPriv.h"
+#include "SkPicturePlayback.h"
 
 // The GrGather device performs GPU-backend-specific preprocessing on
 // a picture. The results are stored in a GPUAccelData.
@@ -243,7 +244,15 @@
     }
 
     virtual void drawPicture(SkPicture& picture) SK_OVERRIDE {
+        // BBH-based rendering doesn't re-issue many of the operations the gather
+        // process cares about (e.g., saves and restores) so it must be disabled.
+        if (NULL != picture.fPlayback) {
+            picture.fPlayback->setUseBBH(false);
+        }
         picture.draw(this);
+        if (NULL != picture.fPlayback) {
+            picture.fPlayback->setUseBBH(true);
+        }
     }
 protected:
     // disable aa for speed