Fix rendering artifacts in pull-saveLayers-forward mode

src/gpu/GrPictureUtils.h

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrPictureUtils_DEFINED
 #define GrPictureUtils_DEFINED
 
 #include "SkPicture.h"
 #include "SkTDArray.h"
 
 // This class encapsulates the GPU-backend-specific acceleration data
 // for a single SkPicture
 class GPUAccelData : public SkPicture::AccelData {
 public:
     // Information about a given saveLayer in an SkPicture
     struct SaveLayerInfo {
         // True if the SaveLayerInfo is valid. False if either 'fOffset' is
         // invalid (due to a non-invertible CTM) or 'fPaint' is NULL (due
         // to a non-copyable paint).
         bool fValid;
         // The size of the saveLayer
         SkISize fSize;
         // The CTM in which this layer's draws must occur. It already incorporates
         // the translation needed to map the layer's top-left point to the origin.
         SkMatrix fCTM;
         // The offset that needs to be passed to drawBitmap to correctly
-        // position the pre-rendered layer.
-        SkPoint fOffset;
+        // position the pre-rendered layer. It is in device space.
+        SkIPoint fOffset;
         // The paint to use on restore. NULL if the paint was not copyable (and
         // thus that this layer should not be pulled forward).
         const SkPaint* fPaint;
         // The ID of this saveLayer in the picture. 0 is an invalid ID.
         size_t  fSaveLayerOpID;
         // The ID of the matching restore in the picture. 0 is an invalid ID.
         size_t  fRestoreOpID;
         // True if this saveLayer has at least one other saveLayer nested within it.
         // False otherwise.
         bool    fHasNestedLayers;
@@ skipping 28 matching lines @@
 
 private:
     SkTDArray<SaveLayerInfo> fSaveLayerInfo;
 
     typedef SkPicture::AccelData INHERITED;
 };
 
 void GatherGPUInfo(SkPicture* pict, GPUAccelData* accelData);
 
 #endif // GrPictureUtils_DEFINED