Use variable length key (rather than accumulated matrix) as save layer hoisting key

src/gpu/GrLayerHoister.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 GrLayerHoister_DEFINED
 #define GrLayerHoister_DEFINED
 
 #include "SkPicture.h"
 #include "SkTDArray.h"
 
 struct GrCachedLayer;
 class GrReplacements;
 struct SkRect;
 
 class GrHoistedLayer {
 public:
-    const SkPicture* fPicture;
+    const SkPicture* fPicture;  // the picture that actually contains the layer
+                                // (not necessarily the top-most picture)
     GrCachedLayer*   fLayer;
     SkIPoint         fOffset;
+    SkMatrix         fInitialMat;
     SkMatrix         fPreMat;
     SkMatrix         fLocalMat;
 };
 
 // This class collects the layer hoisting functionality in one place.
 // For each picture rendering:
 //  FindLayersToHoist should be called once to collect the required layers
 //  DrawLayers should be called once to render them
 //  UnlockLayers should be called once to allow the texture resources to be recycled
 class GrLayerHoister {
@@ skipping 46 matching lines @@
     /** Draw the specified layers into their own individual textures.
         @param context      Owner of the layer cache (and thus the layers)
         @param layers       The layers to be drawn
     */
     static void DrawLayers(GrContext* context, const SkTDArray<GrHoistedLayer>& layers);
 
     /** Convert all the layers in 'layers' into replacement objects in 'replacements'.
         @param layers       The hoisted layers
         @param replacements Replacement object that will be used for a replacement draw
     */
-    static void ConvertLayersToReplacements(const SkTDArray<GrHoistedLayer>& layers,
+    static void ConvertLayersToReplacements(const SkPicture* topLevelPicture, 
+                                            const SkTDArray<GrHoistedLayer>& layers,
                                             GrReplacements* replacements);
 
     /** Unlock a group of layers in the layer cache.
         @param context    Owner of the layer cache (and thus the layers)
         @param layers     Unneeded layers in the atlas
     */
     static void UnlockLayers(GrContext* context, const SkTDArray<GrHoistedLayer>& layers);
 
     /** Forceably remove all cached layers and release the atlas. Useful for debugging and timing.
         This is only functional when GR_CACHE_HOISTED_LAYERS is set to 1 in GrLayerCache.h
         @param context    Owner of the layer cache (and thus the layers)
      */
     static void PurgeCache(GrContext* context);
 };
 
 #endif