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

src/core/SkLayerInfo.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 SkLayerInfo_DEFINED
 #define SkLayerInfo_DEFINED
 
 #include "SkPicture.h"
 #include "SkTArray.h"
 
 // This class stores information about the saveLayer/restore pairs found
 // within an SkPicture. It is used by Ganesh to perform layer hoisting.
 class SkLayerInfo : public SkPicture::AccelData {
 public:
     // Information about a given saveLayer/restore block in an SkPicture
     class BlockInfo {
     public:
-        BlockInfo() : fPicture(NULL), fPaint(NULL) {}
-        ~BlockInfo() { SkSafeUnref(fPicture); SkDELETE(fPaint); }
+        BlockInfo() : fPicture(NULL), fPaint(NULL), fKey(NULL), fKeySize(0) {}
+        ~BlockInfo() { SkSafeUnref(fPicture); SkDELETE(fPaint); SkDELETE_ARRAY(fKey); }
 
         // The picture owning the layer. If the owning picture is the top-most
         // one (i.e., the picture for which this SkLayerInfo was created) then
         // this pointer is NULL. If it is a nested picture then the pointer
         // is non-NULL and owns a ref on the picture.
         const SkPicture* fPicture;
         // The device space bounds of this layer.
         SkRect fBounds;
         // The pre-matrix begins as the identity and accumulates the transforms
         // of the containing SkPictures (if any). This matrix state has to be
@@ skipping 10 matching lines @@
         const SkPaint* fPaint;
         // The index of this saveLayer in the picture.
         size_t  fSaveLayerOpID;
         // The index of the matching restore in the picture.
         size_t  fRestoreOpID;
         // True if this saveLayer has at least one other saveLayer nested within it.
         // False otherwise.
         bool    fHasNestedLayers;
         // True if this saveLayer is nested within another. False otherwise.
         bool    fIsNested;
+        // The variable length key for this saveLayer block. It stores the
+        // thread of drawPicture and saveLayer operation indices that lead to this
+        // saveLayer (including its own op index). The BlockInfo owns this memory.
+        int*    fKey;
+        int     fKeySize;  // # of ints
     };
 
     SkLayerInfo(Key key) : INHERITED(key) { }
 
     BlockInfo& addBlock() { return fBlocks.push_back(); }
 
     int numBlocks() const { return fBlocks.count(); }
 
     const BlockInfo& block(int index) const {
         SkASSERT(index < fBlocks.count());
 
         return fBlocks[index];
     }
 
     // We may, in the future, need to pass in the GPUDevice in order to
     // incorporate the clip and matrix state into the key
     static SkPicture::AccelData::Key ComputeKey();
 
 private:
     SkTArray<BlockInfo, true> fBlocks;
 
     typedef SkPicture::AccelData INHERITED;
 };
 
 #endif // SkLayerInfo_DEFINED